Wetting at polymer surfaces and interfaces

Atomic force microscopy (AFM), neutron reflection (NR) and secondary ion mass spectroscopy (SIMS) are used to examine phase separation in symmetrically segregating thin polymer blend films (≤1000 A). Phase separation in the film leads to undulations of the liquid−air interface, provided the film is sufficiently thin to suppress surface-directed spinodal decomposition waves. Flattened droplets are formed at a very late stage of phase separation, and the aspect ratio of these droplets can be rationalized by an interfacial free energy minimization argument.

http://depts.washington.edu/nanolab/publications/1998Mac.pdf

Phase-Separation-Induced Surface Patterns in Thin Polymer Blend Films

Cluster secondary ion mass spectrometry (cluster SIMS) has played a critical role in the characterization of polymeric materials over the last decade, allowing for the ability to obtain spatially resolved surface and in-depth molecular information from many polymer systems. With the advent of new molecular sources such as , , , and , there are considerable increases in secondary ion signal as compared to more conventional atomic beams (Ar+, Cs+, or Ga+). In addition, compositional depth profiling in organic and polymeric systems is now feasible, without the rapid signal decay that is typically observed under atomic bombardment. The premise behind the success of cluster SIMS is that compared to atomic beams, polyatomic beams tend to cause surface-localized damage with rapid sputter removal rates, resulting in a system at equilibrium, where the damage created is rapidly removed before it can accumulate. Though this may be partly true, there are actually much more complex chemistries occurring under polyatomic bombardment of organic and polymeric materials, which need to be considered and discussed to better understand and define the important parameters for successful depth profiling. The following presents a review of the current literature on polymer analysis using cluster beams. This review will focus on the surface and in-depth characterization of polymer samples with cluster sources, but will also discuss the characterization of other relevant organic materials, and basic polymer radiation chemistry. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:247–293, 2010

Cluster secondary ion mass spectrometry of polymers and related materials.

Polymer surfaces and interfaces have many technological applications. In the present article we review some recent experiments conducted on model systems with the aim of understanding the role played by surface-anchored polymer layers in adhesion and friction. We also discuss some of the related theoretical models. The key parameter for both situations is the degree of interdigitation between the surface layer and the bulk polymer system (an elastomer in the case of adhesion, a molten polymer in the case of friction). We analyze how this degree of interdigitation governs the optimum enhancement in the adhesion energy between the solid wall and an elastomer, and how it is at the origin of the various wall slip regimes observed experimentally.

Surface-Anchored Polymer Chains: Their Role in Adhesion and Friction

Qualitatively different thickness dependences have been observed in the glass transition temperature, Tg, of polystyrene (PS) films supported by hydrogen-passivated silicon (H−Si). It has been suggested that upon annealing at high temperatures in air, the polymer/substrate interface of these films (i.e., PS/Si), though buried underneath the PS layer, might be oxidized, rendering the films a different polymer/substrate interface (i.e., PS/SiOx−Si), which may account for the different thickness dependences of the Tg observed. In this experiment, we examine if the buried substrate interface of PS/H−Si films can indeed be oxidized by annealing the films at 150 °C in air. Our result shows that a residual film does form on top of the H−Si surface, but it is a bound layer of PS. X-ray photoelectron spectroscopic (XPS) analyses and independence of the residual film on the initial PS thickness evidence that the H−Si substrate buried underneath a PS film is not oxidized by annealing. We discuss a possible explanati...

Affinity of Polystyrene Films to Hydrogen-Passivated Silicon and Its Relevance to the Tg of the Films

Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resolution depth profiles in polymer blend thin films and is now regarded as a key probe of surface and interfacial segregation in these systems. Segregation phenomena strongly impact blend properties such as adhesion, friction and weatherability. The strengths and limitations of the SIMS polymer profiling technique are described and contrasted with the complementary techniques of forward recoil elastic scattering (FRES) and neutron reflectivity (NR). The procedures developed for sample preparation and data acquisition are discussed. Experimental results for the effect of incident O2 + energy and angle on depth resolution and sputtering rate in polystyrene (PS) are presented. Ongoing SIMS studies of model blend systems are described: Segregation from dPS (deuterated)/PS blends to vacuum and Si interfaces is examined as a function of the molecular weight of the blend components and preparation of the Si substrate, reve...

Studies of surface and interface segregation in polymer blends by secondary ion mass spectrometry

The concentration profiles of carboxy-terminated polystyrene chains in the melt grafted onto oxide-covered silicon substrates were measured using secondary-ion mass spectroscopy. The grafting density increased with temperature and an enthalpy of +7.4 kcal/mole was deduced for the grafting reaction, SiOH+R(COOH)\ensuremath{\rightleftarrows}R(COOSi)+${\mathrm{H}}_{2}$O. Relatively high grafting densities (\ensuremath{\sigma}\ensuremath{\sim}6.6 mg/${\mathrm{m}}^{2}$) were achieved with minimal chain distortion or displacement of long chains by shorter ones. Significant stretching of the grafted chains occurred for \ensuremath{\sigma}g10 mg/${\mathrm{m}}^{2}$. An equilibrium constant for the grafting reaction incorporating entropy is discussed.

Configuration of grafted polystyrene chains in the melt: Temperature and concentration dependence.

http://repositorio.unicamp.br/jspui/bitstream/REPOSIP/99609/1/2-s2.0-0042625525.pdf

X. Zheng

Papers

Studies of surface and interface segregation in polymer blends by secondary ion mass spectrometry

Configuration of grafted polystyrene chains in the melt: Temperature and concentration dependence.

Configuration Of Grafted Polystyrene Chains In The Melt: Temperature And Concentration Dependence