Direct Probe of Interfacial Structure during Mechanical Contact between Two Polymer Films Using Infrared Visible Sum Frequency Generation Spectroscopy

Harp, Gray P.; Dhinojwala, Ali

doi:10.1080/00218460590944693

Cited by 8 publications

(8 citation statements)

References 22 publications

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“…Figures 2b,c show the SFG results, measured in dry conditions replicating those used in JKR experiments (before, during, and after contact). For both OTS and PVNODC the prominent peaks in the SFG spectra are for ordered terminal methyl groups, 31,36 depicted in Figure 2d, characteristic of low-energy surfaces depicted. The absence of methylene signals indicates an all-trans conformation of the hydrophobic alkyl chains.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The resolution of the spectrometer is estimated to be 5 cm –1 . The resulting spectra were modeled for peak identification using a Lorenztian fitting function where χ eff,NR describes the nonresonant contribution. A q , Γ q , and ω q are the amplitude, damping constant, and angular frequency of the q th vibrational resonance, respectively.…”

Section: Experimental Sectionmentioning

confidence: 99%

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Consequences of Water between Two Hydrophobic Surfaces on Adhesion and Wetting

et al. 2015

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The contact of two hydrophobic surfaces in water is of importance in biology, catalysis, material science, and geology. A tenet of hydrophobic attraction is the release of an ordered water layer, leading to a dry contact between two hydrophobic surfaces. Although the waterfree contact has been inferred from numerous experimental and theoretical studies, this has not been directly measured. 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 selfassembled monolayer, OTS, and a polymer coating, PVNODC). We show that the interfacial structures 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−Dupréequation, 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. This study exemplifies the importance of interstitial water in controlling adhesion and wetting. ■ INTRODUCTIONHydrophobic interactions are used to explain many phenomena prevalent in physical and biological sciences, such as protein folding, 1 self-assembly, 2−6 dewetting, 7 adhesion, 8 friction, 9 adsorption, 10 water transport, 11,12 and chemical reactions. 13 The hydrophobic adhesion is defined as the difference in interfacial energy between two hydrophobic surfaces before and after contact underwater. 14 Experimentally, direct force measurements 15−17 or contact angle measurements 18 have been used to measure adhesion energy where the contact between two hydrophobic surfaces is assumed to be dry. This drying phenomenon has been supported by molecular simulations between hydrophobic surfaces 6,19,20 but never experimentally verified.Recent findings are challenging the concept of dry hydrophobic contact. X-ray crystallography has observed the presence of water within protein cavities of varying hydrophobicity which can affect the strength of protein−ligand binding. 21,22 Simulations have also shown that water can be sequestered between hydrophobic plates with a relatively small centralized hydrophilic patch. 23 Ambiguity also remains as to how dry contact is established underwater. The entropy gained by releasing interstitial water between hydrophobic surfaces prior to contact could be facilitated by a depleted density profile at the hydrophobic water interface, 24,25 the presence of nanobubbles, 26 or the concept of increased fluctuations in interfacial water. 27 To understand the role of water in adhesion and contact angles, we have used surface sensitive sum frequency generation spectroscopy (SFG) to directly study the contact interface between two hydrophobic surfaces underwater....

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Experimental Sectionmentioning

confidence: 99%

Consequences of Water between Two Hydrophobic Surfaces on Adhesion and Wetting

et al. 2015

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“…The origin of such a low friction is considered to be associated with the water absorbed in the gel, 1-4 some of which is squeezed out from the gel under the load and serves as a lubricant layer between the gel and solid surface, resulting in a hydrodynamic lubrication. 5,6 Although the structural information about the interfacial water is important for understanding the role of water for the low frictional properties of hydrogel in contact with a solid and molecular structure of lubricants other than water at solid/solid interfaces has been investigated theoretically [7][8][9] and experimentally, [10][11][12][13][14][15][16][17][18][19][20] no experimental investigations on water structure at gel/solid interfaces have been carried out due to the lack of effective experimental technique.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, sum frequency generation (SFG) spectroscopy has been shown to be a very powerful technique to probe molecular structure at the interface. [18][19][20][21][22][23][24][25][26][27][28][29][30][31] SFG is a second order nonlinear optical process, in which two photons of frequencies o 1 and o 2 generate one photon of sum frequency (o 21 The second order nonlinear processes including SFG are prohibited in media with inversion symmetry under the electric dipole approximation and allowed only at the interface between these media where the inversion symmetry is necessarily broken. By using visible light of fixed wavelength and tunable IR light as two input light sources, SFG spectroscopy can be surface sensitive vibrational spectroscopy as the SFG signal is resonantly enhanced when the energy of IR beam becomes equal to that of a vibrational state of surface species.…”

Section: Introductionmentioning

confidence: 99%

Interfacial water structure at polymer gel/quartz interfaces investigated by sum frequency generation spectroscopy

Noguchi

Minowa

Tominaga

et al. 2008

Phys. Chem. Chem. Phys.

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Interfacial structures of water at polyvinyl alcohol (PVA) and poly(2-acrylamido-2-methypropane) sulfonic acid sodium salt (PNaAMPS)/quartz interfaces were investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at 3200 and 3400 cm(-1), corresponding to the symmetric OH stretching of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching of water in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively, in both cases. The "liquid-like" water became dominant when the PVA gel was pressed against the quartz surface. The relative intensity of the SFG signal due to the "liquid-like" water to that due to the "ice-like water" at the quartz surface modified with a self-assembled monolayer of aminopropyltrimethoxysilane (APS) became higher when the negatively charged PNaMPS gel was contacted to the APS modified quartz surface in a solution of pH = 12, where the surface was negatively charged and electrostatic repulsive interaction and low friction were present between the PNaMPS gel and the APS modified surface. It, however, did not change in a solution of pH = 2, where the surface was positively charged and electrostatic attractive interaction and very high friction were present between the PNaMPS gel and the APS modified surface. These results suggest the important role of water structure for small friction at the polymer gel/solid interface.

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“…35 Triangular prism and hemi-cylinder prism are also frequently used to enhance the reflectivity of SFG signal at buried polymer interfaces (Figure 5b and 5c). [36][37][38][39][40][41] However, for the study of polymer surface in air, the prism geometry could also detect strong signal from the buried polymer/prism interface. 42 A trapezoid Dove prism has been used to achieve a multi-reflection geometry surfaces (Figure 5d).…”

Section: Experimental Geometries and Substrates Used In Sum Frequency Generation Vibrational Spectroscopymentioning

confidence: 99%

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

Zhang

2017

Appl Spectrosc

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Sum frequency generation vibrational spectroscopy (SFG-VS) has become one of the most appealing technologies to characterize molecular structures at interfaces. In this focal point review, we focus on SFG-VS studies at buried polymer interfaces and review many of the recent publications in the field. We also cover the essential theoretical background of SFG-VS and discuss the experimental implementation of SFG-VS.

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Direct Probe of Interfacial Structure during Mechanical Contact between Two Polymer Films Using Infrared Visible Sum Frequency Generation Spectroscopy

Cited by 8 publications

References 22 publications

Consequences of Water between Two Hydrophobic Surfaces on Adhesion and Wetting

Consequences of Water between Two Hydrophobic Surfaces on Adhesion and Wetting

Interfacial water structure at polymer gel/quartz interfaces investigated by sum frequency generation spectroscopy

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

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