Interfacial molecular structure

Attractive or repulsive interaction between two solid surfaces should play an important role in the interfacial frictional behavior [87,92-95]. From previous theoretical [89] and experimental investigations [87, 95], it was known that the attractive interaction result in a high friction and repulsive interaction results in low friction force. To characterize the interfacial molecular structure between two solids under electrostatic interaction is also important to elucidate the frictional properties of two solids. 

Lee and Char [93] studied the reinforcement of the interface between an amorphous polyamide (PA) and polystyrene with the addition of thin layers of a random copolymer of styrene-maleic anhydride (with 8% MA) sandwiched at the interface. After annealing above the Tg of PS, they found significantly higher values of Qc for samples prepared with thinner layers of SMA than for the thicker ones. They initially rationalized their results by invoking the competition between the reaction rate at the interface and the diffusion rate of the SMA away from the interface. For very thick layers, and therefore also for pure SMA, the reaction rate was much faster than the diffusion rate away from the interface and favored therefore a multiple stitching architecture, as shown schematically in Fig. 50. Such an interfacial molecular structure does not favor good entanglements with the homopolymer and is mechanically weak. 

In this section, after an introduction on theory and experimental setup of SFG, we will briefly review some recent results of SFG studies on the interfacial molecular structure of the solid surface modified by organic thin Aims. It should be mentioned here that SFG is still in its infancy compared to infrared and Raman spectroscopy. More efforts including theoretical analysis [28-33] are required to understand its real capability and to make this method as a routine spectroscopic technique. 

As mentioned earlier, SFG is now widely applied in different fields. Table 1 briefly summarizes the SFG studies carried out in some groups. Owing to the specialized purpose and page limitation of the review, we will concentrate our interest on the study of the interfacial molecular structure on the modified solid surfaces by SAM and LB films, both in air and in... 

Recently, Cremer et al. showed interesting experimental results, which demonstrates the water structures on the surface of an eicosanoic acid LB monolayer on air/water interface significantly affected by the existence of divalent metal ions (Zn " " and Mg +) [227]. The effect of the metal divalent cations on the interfacial molecular structures of the LB films is a very attractive subject to be investigated in detail. 

As briefly reviewed in this section, SFG vibrational technique has significant advantages to the conventional vibrational spectroscopy. A great deal of new information on the interfacial molecular structure will be elucidated by this method, which is important and useful for understanding and controlling the surface property and fimctionality of materials. Appearance of the new techniques such as SFG imaging as well as FT-SFG will make this method more powerful and more easy to use. It is also expected that more theoretical studies will be carried out to quantitatively understand all the information we can get from SFG measurements and to anticipate what we can further obtain from this method. 

Lachman, N. and Wagner, D. H. (2010) Correlation between interfacial molecular structure and mechanics in CNT/epoxy nano-composites . Composites Part A Applied Science and Manufacturing, 41, 1093-1098. 

Numerical methods with different time- and length scales are employed and developed to investigate material properties and behaviors. Among them, molecular modeling can predict the molecular behaviors and correlate macroscopic properties of a material with various variables. The most popular techniques include molecular mechanics (MM), MD, and Monte Carlo (MC) simulation. These techniques are now routinely used to investigate the structure, dynamics, and thermodynamics of inorganic, biological, and polymer systems. They have recently been used to predict the thermodynamic and kinetic properties of nanoparticle-matrix mixtures, interfacial molecular structure and interactions, molecular dynamic properties, and mechanical properties. 

Hydropolymer gel has been considered as a possible candidate for an artificial articular cartilage in artificial joints because it exhibits very low friction when it is in contact with a solid. The origin of such low friction is considered to be associated with the water absorbed in the gel [83-86], 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 hydrodynamic lubrication [87, 88]. Although the structural information about the interfacial water is important to understand the role of water for the low frictional properties of hydrogel in contact with a solid and the molecular structure of lubricants other than water at solid/solid interfaces have been investigated theoretically [89-91] and experimentally [92-98], no experimental investigations on water structure at gel/solid interfaces have been carried out due to the lack of an effective experimental technique. 

One of the most attractive roles of liquid liquid interfaces that we found in solvent extraction kinetics of metal ions is a catalytic effect. Shaking or stirring of the solvent extraction system generates a wide interfacial area or a large specific interfacial area defined as the interfacial area divided by a bulk phase volume. Metal extractants have a molecular structure which has both hydrophilic and hydrophobic groups. Therefore, they have a property of interfacial adsorptivity much like surfactant molecules. Adsorption of extractant at the liquid liquid interface can dramatically facilitate the interfacial com-plexation which has been exploited from our research. 

This finding a new type of catalysis will provide a useful hint for the design of molecular structures of interfacially adsorbable and strongly reactive ligands for a speeifie metal ion. 

A brief review is given of the important qualitative features of thermoplastic elastomers. Particular emphasis is given to the molecular structure, bulk morphology and interfacial character of these materials. Both equilibrium and nonequilibrium structures are discussed... 

A major emerging area of research activity in interfacial electrochemistry concerns the development of in-situ surface spectroscopic methods, especially those applicable in conventional electrochemical circumstances. One central objective is to obtain detailed molecular structural information for species within the double layer to complement the inherently macroscopic information that is extracted from conventional electrochemical techniques. Vibrational spectroscopic methods are particularly valuable for this purpose in view of their sensitivity to the nature of intermolecular interactions and surface bonding as well as to molecular structure. Two such techniques have been demonstrated to be useful in electrochemical systems surface-enhanced Raman spectroscopy... 

It is for this reason that spectroscopy offers the only experimental method for characterizing the interfacial region that is not automatically destined to run into basic conceptual difficulties. This is not to say that difficulties of a technical nature will not arise (40-48), nor that the conceptual difficulty of differing time scales among spectroscopic techniques will cause no problems (50). Nonetheless, it is to be hoped that future investigations of sorption reactions will focus more on probing the molecular structure of the mineral/water interface than on attempting simply to divine what the structure may be. 

Complementary to using repulsive interactions in order to achieve shape control, attractive interactions of relatively large building blocks, which are rationally designed regarding their shape, polarity, and functional groups, can be employed for intramolecular self-assembly [23]. In this case, the molecular structure optimizes itself to realize specific interactions between the blocks and minimize the interfacial energy. 

Molecular Structure Effects and Detergency. The correlation of surfactant structure with interfacial and colloid properties is a poorly understood science. Much study in this area has been thermodynamic which has been a useful endeavor but which nevertheless fails to provide specific molecular structure/physical property correlations. The following study has also been largely thermodynamic to this point however, since the data has been collected on pure LAS homologs, it provides an opportunity to apply some of the quasi-thermodynamic treatments that have been proffered in the literature to date. 

In solution, block copolymers display interesting colloidal and interfacial properties. They can be used as emulsifying agents in water-oil and oil-oil systems (6 ). In the later case, the oil phases are solid and they give rise to polymeric alloys (7.) or they are liquid and they allow the preparation of latexes in organic medium (8 ). However, the molecular structure of block copolymers based on polybutadiene PB (70 ) and polystyrene PS behave as thermoplastic elastomers when engaged in multiblock (PB-PS)n or triblock (PS-PB-PS) structures but never when implied in inverse triblock or diblock arrangements. Similarly the... 

In all adhesive joints, the interfacial region between the adhesive and the substrate plays an important role in the transfer of stress from one adherend to another [8]. The initial strength and stability of the joint depend on the molecular structure of the interphase after processing and environmental exposure, respectively. Characterization of the molecular structure near the interface is essential to model and, subsequently, to maximize the performance of an adhesive system in a given environment. When deposited on a substrate, the silane primers have a finite thickness and constitute separate phases. If there is interaction between the primer and the adherend surface or adhesive, a new interphase region is formed. This interphase has a molecular structure different from the molecular structure of either of the two primary phases from which it is formed. Thus, it is essential to characterize these interphases thoroughly. 

Our interest in SERS stemmed from our research activities concerned with establishing connections between the molecular structure of electrode interfaces and electrochemical reactivity. A current objective of our group is to employ SERS as a molecular probe of adsorbate-surface interactions to systems of relevance to electrochemical processes, and to examine the interfacial molecular changes brought about by electrochemical reactions. The combination of SERS and conventional electrochemical techniques can in principle yield a detailed picture of interfacial processes since the latter provides a sensitive monitor of the electron transfer and electronic redistributions associated with the surface molecular changes probed by the former. Although few such applications of SERS have been reported so far the approaches appear to have considerable promise. 

Electrodes represent an unrivaled platform onto which interfacial supramolecular structures can be assembled. They can be fully characterized before assembly and offer a convenient means to both probe and control the properties of the film. The interest in this area has increased dramatically in recent years because adsorbed monolayers enable both the nature of the chemical functional groups and their topology to be controlled. This molecular-level control allows the effects of both chemical and geometric properties on electron transfer rates to be explored. Moreover, these assemblies underpin technologies ranging from electrocatalysis to redox-switchable non-linear optical materials. 

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