Doctor of Philosophy, The Ohio State University, 2007, Chemistry

The uptake and reaction of methanol at the air-liquid interface of 0-96.5 wt% sulfuric acid (SA) solutions has been observed directly using vibrational sum frequency generation spectroscopy (VSFG) and Raman spectroscopy. Evidence for the formation of methyl hydrogen sulfate (MHS) was obtained by the presence of a new peak in the 800 cm-1 region, not present in either the neat methanol or concentrated sulfuric acid spectra. This peak is attributed to the singly bonded OSO symmetric stretch of MHS. The maximum yield of MHS with a large SA excess is shown to be (95±5)% at –(15±2)°C. No evidence was found to suggest formation of dimethyl sulfate. As the concentration of SA increases from 0–96.5 wt%, the SFG spectra shift from that of methanol to that of methyl hydrogen sulfate. The surface is saturated with a mixture of the three methyl compounds after 15 minutes, although the relative amounts of MeOH, MeOH2+, and MHS vary with SA concentration. Uptake occurred on a much longer timescale, suggesting that uptake of methanol by sulfuric acid solutions is diffusion-limited. The diffusion coefficients for methanol into 0–96.5 wt% sulfuric acid solutions were measured by passing MeOH vapor in N2over the SA solutions and monitoring the uptake using Raman spectroscopy. The value obtained for methanol into water, D = (0.7±0.2) x 10-5cm2/s, is in agreement with values found in the literature. The values of D in 39.2-96.5 wt% SA range from (1–2.7) x 10-6cm2/s with the maximum value occurring for the 59.5 wt% SA solution. This may be due to the speciation of MeOH in the SA solutions or to speciation of the SA solutions. The organization of 1-butanol and 1-hexanol, at air-liquid interfaces was investigated using VSFG. There is evidence for centrosymmetric structures at the surface of pure butanol and hexanol. At most solution surfaces, butanol molecules organize in all-trans conformations. In contrast, the spectrum of 0.052 M butanol in 59.5 wt% sulfuric acid solution possesses a s (open full item for complete abstract)

Committee: Heather Allen (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

Many important processes such as friction, adhesion, wetting, and adsorption that are relevant to a wide, multidisciplinary community and industries occur at material interfaces. What traditional methods to characterize these interfacial properties often lack is the ability to obtain direct, in situ molecular information which can be correlated to the property of interest. Vibrational spectroscopy tools such as attenuated total reflectance infrared (ATR-IR) and sum frequency generation (SFG) spectroscopy represent methods that, with some ingenuity, allow us to obtain this information for any surface or interface which is optically accessible. While SFG represents a highly surface/interface-specific technique, ATR-IR provides information up to 1 micron within a sample; thus, the two methods can be complementary. Between these two methods, new information can be gained for a variety of material interfaces. To this end, we have first employed SFG and ATR-IR together to quantify the “real” contact area, or the area over which materials make molecular contact. Results highlight the effectiveness of these tools in terms of sensitivity compared to other methods and provide evidence of the extent of molecular contact for systems of varying roughness and modulus. Additionally, we use SFG and ATR-IR to connect the molecular-scale picture of a polyelectrolyte (charge-bearing) brush as it absorbs water in humid air and relate these properties to sliding friction. Results of this investigation reveal a new transition phenomenon to create sharply switchable friction, and its link to the molecular-scale structure of the brush. Finally, we employ ATR-IR in a more applied sense in an attempt to quantitively analyze the concentration of additives on the surface of rubber compounds. Our investigation highlights the potential usefulness of FTIR spectroscopy in general for rapid quantitative analysis directly on samples of interest without any prior chemical separation.

Committee: Ali Dhinojwala (Advisor); Fardin Khabaz (Committee Chair); Kevin Cavicchi (Committee Member); Abraham Joy (Committee Member); Jutta Luettmer-Strathmann (Committee Member) Subjects: Materials Science; Physical Chemistry; Physics

Doctor of Philosophy (PhD), Ohio University, 2022, Chemical Engineering (Engineering and Technology)

Electrochemical nitrogen reduction has been proposed as a potential means of generating ammonia sustainably in comparison with the current industrial process. The possibility of using green hydrogen sources to produce nitrogen would allow for the production of this vital molecule while producing much less greenhouse gas. Significant challenges must be addressed for an electrochemical ammonia synthesis process to become feasible, most notably the dominance of the competing hydrogen evolution reaction which prevents the efficient reduction of nitrogen to ammonia. The effect of catalyst loading, temperature, and applied potential was tested on the nitrogen reduction reaction (NRR) using Pt and Ir catalysts in an electrochemical cell using an alkaline polymer gel electrolyte. It was hypothesized that the polymer gel electrolyte would limit the transport of water in the electrolyte and thus inhibit the competing HER. Pt and Ir nanoparticle electrocatalysts were synthesized and deposited on carbon gas diffusion electrodes. The ammonia was quantified by conversion to indophenol and testing via UV-Vis absorption spectroscopy. The generation of ammonia with both catalysts was demonstrated, and the reaction parameters tested were determined not to have a statistically significant impact on the results. While considering alternative catalysts for the NRR, it became clear that some contamination was contributing to false positive signals, thus a number of different possible sources of false positive signal were tested. Residual ammonia in the humidifier in the NRR reaction setup was quantified, and steps were taken in the experimental process to mitigate this issue. Degradation of the ionomer binding agent used in the electrodes was also tested, and deemed unlikely to be a contributor to the observed contamination. Finally, a series of blank tests were run which revealed intermittent ammonia contamination, which was attributed to ambient atmospheric ammonia contamination (open full item for complete abstract)

Committee: Gerardine Botte (Advisor); Valerie Young (Advisor); Savas Kaya (Committee Member); Howard Dewald (Committee Member); John Staser (Committee Member); Katherine Cimatu (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, University of Akron, 2021, Polymer Science

Interfacial interactions govern phenomena such as adsorption, wetting, and adhesion. These interactions can be broken down into two categories: van der Waals and polar interactions. A subset of polar interactions is acid-base interaction. Here, I continue to expand on Drago-Wayland and Badger-Bauer framework demonstrated in previous literature to a planar silicon dioxide surface. Sum frequency generation spectroscopy is used to determine the frequency shift between the acid (silicon dioxide) and a series of bases in the pursuit of determining the Ea and Ca parameter for the planar silicon dioxide surface. These parameters are juxtaposed with previously reported Drago-Wayland values for silicon dioxide and sapphire. Additionally, competitive adsorption of a binary mixture on silicon dioxide is examined by SFG. The interfacial composition is used to calculate an adsorption isotherm and the resultant interfacial energy is compared to the interfacial energy calculated by a thermodynamic approach. Additionally, interfacial interactions between water and polymers can affect the polymers interfacial structure which can result in product failure like biomedical incompatibility, adhesive failure and delamination of coatings. Contact angle has been used since the 18th century to probe interfacial information between liquids and substrates. Here, I propose that additional measurements taken in tandem with contact angle enable a better understanding of interfacial rearrangement and simultaneously reveal an interesting phenomena due to annealing temperature of polymer films.

Committee: Ali Dhinojwala (Advisor); Mesfin Tsige (Committee Chair); Toshikazu Miyoshi (Committee Member); Abraham Joy (Committee Member); Adam Smith (Committee Member) Subjects: Materials Science; Polymers

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

Herein I describe Vibrational Sum Frequency Generation, a non-linear spectroscopy with vibrational specificity and high sensitivity for buried interfaces. I describe work to extend Vibration Sum Frequency Generation to electrochemical interfaces using Surface Plasmon Resonance. Using this method, I can detect molecules across the vibrational region at current densities greater than 1 mA/cm2 and with detection limits as low as 1% of a monolayer. During carbon dioxide reduction on gold electrodes I observe atop CO, a surface intermediate. Using Stark spectroscopy of the CO intermediate I measure the potential dependent interfacial electric field. I also prescribe a way to account for dipole-dipole and third order contributions to the SFG signal and comment on potential dependent intensity and coverage changes. Correlations between Stark field measurements and the SFG Intensity reveal potential dependent changes to the double layer structure that favor carbon dioxide reduction. I find that cite blocking by electrolyte cations lowers the steady state coverage of CO, but that its presence increases carbon dioxide reduction activity. Stark spectroscopy of several cations reveals that the increase in activity is not related to the magnitude of the interfacial electric field but is instead related to specific interactions of the hydrated cations with intermediates. Preliminary measurements of interfacial water also show differences between cations, which may corroborate these findings.

Committee: Robert Baker (Advisor); Heather Allen (Committee Chair); James Coe (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2021, Polymer Science

Adhesives are a vital part of our daily life. In the morning, we are awakened with alarm clocks that are stuck together by glues and at night, the smartphones we scroll through are assembled with adhesive interfaces. However, most of the commercial adhesives fail to adhere in the presence of moist air or water. This inability of manmade adhesives to stick in the presence of water is ironic, given that our body is stuck together with billions of adhesive joints in wet conditions. In the past, the presence of moisture and water was prevented at least until the curing of the adhesive. But, the recent advancements in tissue engineering, robotics, and electronics calls for adhesives that can stick in the presence of water for their performance in unprecedented environments. Though manmade adhesives fail to adhere in the presence of water, aquatic organisms such as mussels and sandcastle worms create robust underwater adhesives to sustain their life near tide-swept shores. Inspired by the adhesive mechanisms of aquatic organisms, herein we created three generations of underwater adhesives. The underwater adhesives created in this study are devoid of toxic organic solvents and crosslinkers to optimize the use in a biomedical setting. Using a combination of synthetic chemistry, interfacial adhesion measurements, spectroscopy, and simulations, a structure-underwater adhesion relationship was determined. It was found that parameters such as interfacial interactions, hydrophobicity, and viscosity of the adhesive are important while creating underwater adhesives.

Committee: Abraham Joy (Advisor); Ali Dhinojwala (Committee Chair); Mesfin Tsige (Committee Member); Junpeng Wang (Committee Member); Newby Bi-Min (Committee Member) Subjects: Biomedical Engineering; Chemical Engineering; Chemistry; Condensation; Materials Science; Nanoscience; Nanotechnology; Organic Chemistry; Polymer Chemistry; Polymers

Doctor of Philosophy (PhD), Ohio University, 2020, Chemistry and Biochemistry (Arts and Sciences)

Investigating the specific local environment and molecular interactions at liquid surfaces is crucial in comprehending physical, chemical, and biological processes. Probing the interfacial molecular conformations will provide an insight into the relationship between surface structure and the governing interactions at the surface. Herein, this dissertation used the approach of the effect of substituents on the interfacial conformation of a methacrylate backbone, to observe such surface structure interaction relationships. The ethyl end of the methacrylate monomer was substituted with bulky groups and electron-withdrawing groups. These substituted monomers were synthesized via nucleophilic addition elimination reaction and characterized using sum frequency generation (SFG) spectroscopy at the air-liquid interface. The spectroscopic results were correlated with surface tension measurements and the overall dipole moment of the molecules. The presence of bulky substituents affected the orientation distribution of the interfacial molecules. On the other hand, in the presence of electron-withdrawing groups, the intensity of vibrational modes was affected, suggesting the changes in interfacial molecular conformations and existing intermolecular interactions. In another project, quaternary ammonium surfactants were utilized to assess their conformation and orientation at the air-water interface using SFG spectroscopy. Herein, the approach of solvent isotopic substitution was used to investigate the surfactant water interactions. The results showed the addition of deuterated water rearranges its head group parallel to the interface and straightens its chain with reduced gauche defects. The change in the conformation of the surfactant molecules at the air-liquid interface showcased the difference in intermolecular interactions for water and deuterated water. In summary, these studies revealed the importance of SFG spectroscopy as a tool to probe surface structures in gauging m (open full item for complete abstract)

Committee: Katherine Cimatu (Advisor) Subjects: Chemistry; Molecules; Optics; Physical Chemistry; Polymers

Doctor of Philosophy (PhD), Ohio University, 2019, Chemistry and Biochemistry (Arts and Sciences)

The research work presented here utilizes the second order non-linear optical sum frequency generation (SFG) vibrational spectroscopy to study interfacial molecular organization. This spectroscopic technique is intrinsically selective to the anisotropic dipoles present at the interface. The main objective of this study is to investigate the molecular organization of the methacrylate-based monomers at both the hydrophilic and hydrophilic solid-liquid interface and thin films of the polymers at air-solid and air-liquid interfaces. The ethyl methacrylate monomers used in the study presented here have varied substituent groups at the ethyl group. Different types of substituents are introduced to study for example the effect of size or electronegativity of the substituents on the conformation of the monomers at the interface. This dissertation explores the effect of the bulky and the electronegative substituent groups on the organization of monomers at both the hydrophilic and hydrophobic solid-monomer interface. When the results of the monomers are compared to the results at the air-monomer interface, we found that the monomer conformation is different at the hydrophilic solid-interface. This difference can be due to a change of the environment and the existence of hydrogen bonding between carbonyl groups of the monomers and the silanol groups of the hydrophilic silica. The SFG signal from carbonyl groups of the monomer was found to be affected by the size and the electronegativity of the substituents. In general, the smaller the size or the weaker the electronegativity of the substituent group, the stronger is the carbonyl signal. Also, in the hydrophobic solid-monomer interface study, regardless of the nature of the substituents, no appreciable carbonyl signal was observed. This observation indicates that the surface silanol group provides hydrogen bonding avenues to the carbonyl groups of the monomers and hence, there is the net orientation of the carbonyl group (open full item for complete abstract)

Committee: Katherine Cimatu (Advisor) Subjects: Chemistry; Materials Science; Physical Chemistry; Polymers

Doctor of Philosophy, The Ohio State University, 2016, Chemistry

Sea spray aerosols (SSA) impact Earth's climate directly and indirectly by scattering and absorbing solar radiation and influencing cloud formation, respectively. SSA are formed through the wind-drive wave action at the ocean surface, and their chemical composition is impacted by the biological activity in the sea surface microlayer (SSML), the thin organic layer present at the air-ocean interface. Physical and optical properties of SSA are influenced by the structure and organization of their surfaces. Organic films are known to form at the surface of SSA, and therefore a molecular-level understanding of the organic species that make up these films and their subsequent impact on interfacial properties is necessary to gain insight into climate change. In this dissertation Langmuir monolayers are utilized as proxies for organic-coated SSA. Phase behavior, rigidity, and stability of monolayers are assessed with surface pressure-area isotherms. Surface morphology of monolayers was imaged with Brewster angle microscopy (BAM). Infrared reflection-absorption spectroscopy (IRRAS) and vibrational sum frequency generation (VSFG) spectroscopy were used to examine the molecular-level structure and intermolecular interactions of the monolayers. VSFG was additionally used to probe the organization and structure of water molecules in the interfacial region. As SSA are chemically complex, several different types of atmospherically-relevant lipid-aqueous interfaces are investigated. The effect of ion enrichment for marine-relevant cations (Na+, Mg2+, Ca2+, and K+) on the interfacial properties of the phospholipid dipalmitoylphosphatidylcholine (DPPC) was investigated. All cations were found to impact monolayer properties, with divalent cations having a greater effect than monovalent ions. Refractive index of the monolayer was found to decrease with increasing cation concentration. In the case of Ca2+, significant dehydration of the phosphate headgroup was observed. Bindin (open full item for complete abstract)

Committee: Heather Allen (Advisor) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2016, Polymer Science

The role of water is often overlooked in interfacial phenomena, but its presence influences many interfacial processes relevant to a number of scientific disciplines. Direct force measurements have offered the most insight into underwater surface related phenomena such as adhesion, wetting, and friction, and have provided molecular descriptions to the physical interactions taking place at the contact interface. Although the insight from these experiments maybe true, there lacks direct molecular confirmation of the assertions interpreted from these force measurements. To address this, we have studied the impact of water on adhesion, friction, and wetting by using a suite of complementary surface sensitive techniques. By using non-linear sum frequency generation spectroscopy, we are able to probe surfaces at a molecular level and connect these chemical details to better understand interfacial phenomena. This thesis focuses on three studies to better understand the role of water in interfacial phenomena. For the first study, we focused on the contact of two hydrophobic surfaces in water. Here, we use surface sensitive sum frequency generation spectroscopy to directly probe the contact interface between hydrophobic poly-(dimethylsiloxane) (PDMS) and two hydrophobic surfaces (a self-assembled monolayer, OTS, and a polymer coating, PVNODC). We show that the interfacial structure for OTS and PVNODC are identical in dry contact but that they differ dramatically in wet contact. In water, the PVNODC surface partially rearranges at grain boundaries, trapping water at the contact interface leading to a 50% reduction in adhesion energy compared to OTS-PDMS contact. The Young-Dupr\'e equation, used extensively to calculate the thermodynamic work of adhesion, predicts no differences between the adhesion energy for these two hydrophobic surfaces, indicating a failure of this well-known equation when there is a heterogeneous contact. For the second study, we studied (open full item for complete abstract)

Committee: Ali Dhinojwala (Advisor); Matthew Becker (Advisor); Abraham Joy (Committee Member); Mesfin Tsige (Committee Chair); Andrey Dobrynin (Committee Member); Adam Smith (Committee Member) Subjects: Physical Chemistry; Polymers

Doctor of Philosophy, The Ohio State University, 2010, Chemistry

Marine aerosols have direct effects on the physics and chemistry of marine atmosphere. In a global dimension, marine aerosols are a key factor in controlling the global climate change by scattering and absorbing solar radiations. Because of limited understanding of interfacial molecular structure and heterogeneous chemistry, model studies of fatty acid monolayers at the air-liquid interface are capable of providing new insight into the aerosol chemistry. In this dissertation, a broad bandwidth sum frequency generation (BBSFG) vibrational technique was used to investigate surface structure, organization, and solvation of monolayer systems on aqueous surfaces. The first molecule of interest is palmitic acid (PA, C16). One of the key findings is that deprotonation can be initiated by ionic binding to the fatty acid headgroups, even at neutral pH. The binding affinity increases in the order that Na+ ~ Mg2+ < K+ < Ca2+. However, the binding of these four cations has little effect on the order and the orientation of the acyl chain in PA with respect to pure water. In addition, the interfacial water structures underneath the PA monolayers also reveal considerable spectral transformations when exposed to Mg2+ and Ca2+. At low concentration (0.1M), three bands were observed in the hydrogen bonding region: ~3600 cm-1 (hydrogen-bonded fatty acid headgroups), ~3400 cm-1 (weakly hydrogen-bonded water molecules), and ~3200 cm-1 (strongly hydrogen-bonded water molecules). At 0.3 M, the intensities of these three bands start to decrease for Mg2+ and Ca2+. However, in concentrated Mg2+ and Ca2+ solutions (~2.0 M), the ~3400 cm-1 band and the ~3200 cm-1 band start to converge and to peak at 3300 cm-1 with enhanced intensity. This may suggest that there is significant water restructuring in the course of increasing concentration due to charge neutralization effects at the surface. More importantly, at concentrated conditions, the already disrupted hydrogen-bonding network reorganizes (open full item for complete abstract)

Committee: Heather Allen PhD (Advisor); Christopher Hadad PhD (Committee Member); Anne McCoy PhD (Committee Member); Thomas Sydnor PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Akron, 2011, Polymer Science

Interfaces are important in many areas including adhesion, friction, coatings, nanocomposites, heat transfer, biomedical implants and cell biology. Most interfacial experiments involve force measurements and, consequently, molecular models to explain the force results. To make progress in this field, it is necessary to understand the structure of interfacial molecules in direct contact. Here, we have used the interface sensitivity of infrared-visible sum frequency generation spectroscopy (SFG) to probe the molecular structure of contact and sliding interfaces in-situ along with force measurements. SFG is a second order nonlinear optical technique that provides information on the chemical structure, orientation and concentration of molecules at interfaces. Two types of interfaces are probed in the current study. The initial two studies focus on static interfaces and the remaining three on dynamic interfaces. In the first investigation, we have studied polar interactions at solid-liquid and solid-solid interfaces using SFG spectroscopy. The shift of the sapphire surface hydroxyl peak in contact with several polar and non-polar liquids and polymers is used to determine the interaction energy. The trend in the interaction energies cannot be explained by only measuring water contact angles. Molecular rearrangements at the sapphire interface, to maximize the acid-base interactions, play a dominant role and these effects are not accounted for in the current theoretical models. The second investigation probes the interactions of polystyrene (PS)-poly(methyl methacrylate) (PMMA) blends with a sapphire surface. The acid-base interaction of carboxyl groups with surface hydroxyl groups is a strong driving force for segregation of PMMA next to the sapphire surface. Even with 0.005 weight fraction of PMMA in the blend, the concentration at the sapphire-blend interface is similar to that of bulk PMMA. This result is significant for understanding and controlling the interfaces res (open full item for complete abstract)

Committee: Ali Dhinojwala Dr. (Advisor); Mark Foster Dr. (Committee Chair); Gary Hamed Dr. (Committee Member); Alamgir Karim Dr. (Committee Member); Jutta Strathmann Dr. (Committee Member) Subjects: Materials Science; Physical Chemistry; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2007, Polymer Science

Friction and wear are important technologically. Tires on wet roads, windshield wipers and human joints are examples where nanometer-thick liquids are confined between flexible-rigid contact interfaces. Fundamental understanding of the structure of these liquids can assist in the design of products such as artificial joints and lubricants for Micro-electromechanical systems [MEMS]. Prior force measurements have suggested an increase in apparent viscosity of confined liquid and sometimes solid-like responses. But, these have not given the state of molecules under confinement. In the present study, we have used a surface sensitive, non-linear optical technique (infrared-visible sum frequency generation spectroscopy [SFG]) to investigate molecular structure at hidden interfaces. SFG can identify chemical groups, concentration and orientation of molecules at an interface. A friction cell was developed to study sliding of a smooth elastomeric lens against a sapphire surface. Experiments were done with dry sliding as well as lubricated sliding in the presence of linear alkane liquids. SFG spectra at the alkane / sapphire interface revealed ordering of the confined alkane molecules. These were more ordered than alkane liquid, but less ordered than alkane crystal. Cooling of the confined alkane below its melting temperature [TM] led to molecular orientation that was different from that of bulk crystal next to a sapphire surface. Molecules were oriented with their symmetry axis parallel to the surface normal. In addition, the melting temperature [Tconf] under confinement for a series of linear alkanes (n =15 - 27) showed a surprising trend. Intermediate molecular weights showed melting point depression. The Tconf values suggested that melting started at the alkane / sapphire interface. In another investigation, confinement of water between an elastomeric PDMS lens and sapphire was studied. SFG spectra at the sapphire / water / PDMS interface revealed a heterogeneous morphol (open full item for complete abstract)

Committee: Ali Dhinojwala (Advisor) Subjects: Chemistry, Physical; Chemistry, Polymer; Engineering, Materials Science; Physics, Condensed Matter; Physics, Optics

Doctor of Philosophy, University of Akron, 2006, Polymer Science

We have studied the contact interface between elastomeric poly(dimethyl siloxane) (PDMS) lenses with various solid surfaces during adhesion and friction using IR-visible sum frequency generation spectroscopy (SFG). SFG in total internal reflection (TIR) geometry can be used to determine molecular structure at the polymer/solid and polymer/polymer contact interfaces. It is a nonlinear optical technique, which detects the orientation and density of molecules at interfaces. In this study, we have designed a novel approach to couple SFG with adhesion and friction experiments. The solid surfaces were chosen to be octadecytrichlorosilane monolayer (OTS), poly(vinyl n-octadecyl carbamate-co-vinyl acetate) (PVNODC), polystyrene (PS), poly(n-butyl methacrylate) (PnBMA), and poly(n-propyl methacrylate) (PnPMA). In the first part of the research, we have concentrated on the importance of characterizing the static contact interface in relation to adhesion. Our results for the OTS in contact with oxygen plasma treated PDMS show surprising surface restructuring, which results in adhesion hysteresis. The short PDMS chains generated during plasma treatment are locally confined and are as strongly ordered as OTS. SFG spectra from other surfaces (sapphire substrates and fluorinated monolayers (FC)) indicates that short PDMS chains require not only confinement but also an ordered template provided by the methyl groups of OTS. In the second part, we have studied the sliding contact interfaces of various polymers with PDMS. The friction forces between PDMS lenses and glassy PS are about four times higher than PDMS sliding on crystalline well-packed PVNODC surfaces. This cannot be explained by the difference in adhesion energy or hysteresis. The in-situ SFG measurements indicate local interdigitation during contact, which is evident from the change in orientation of PS phenyl groups upon mechanical contact and during sliding compared to that at the PS surface. Such a local penetratio (open full item for complete abstract)

Committee: Ali Dhinojwala (Advisor) Subjects: Chemistry, Polymer