Polymers surface nature

D Souza, S.M. Alexander, C. Carr, S.W. Waller, A.M. Whitcombe, M.J. Vulfson, E.N. Directed nucleation of calcite at a crystal-imprinted polymer surface. Nature... 

Takezawa, T., Mori, Y, Yoshizato, K. (1990). CeU culture on a thermo-responsive polymer surface. Nature Biotechnology, 8, 854-856. 

Klein J ef a/1994 Reduction of frictional forces between solid surfaces bearing polymer brushes Nature 370 634-7... 

Thickeners. Thickeners are added to remover formulas to increase the viscosity which allows the remover to cling to vertical surfaces. Natural and synthetic polymers are used as thickeners. They are generally dispersed and then caused to swell by the addition of a protic solvent or by adjusting the pH of the remover. When the polymer swells, it causes the viscosity of the mixture to increase. Viscosity is controlled by the amount of thickener added. Common thickeners used in organic removers include hydroxypropylmethylceUulose [9004-65-3], hydroxypropylceUulose [9004-64-2], hydroxyethyl cellulose, and poly(acryHc acid) [9003-01-4]. Thickeners used in aqueous removers include acryHc polymers and latex-type polymers. Some thickeners are not stable in very acidic or very basic environments, so careful selection is important. 

Poljraer surfaces can be easily modified with microwave or radio-frequency-energized glow discharge techniques. The polymer surface cross-links or oxidizes, depending on the nature of the plasma atmosphere. Oxidizing (oxygen) and nonoxidizing (helium) plasmas can have a wide variety of effects on polymer surface wettability characteristics (92). 

Wool [32] has considered the fractal nature of polymer-metal and of polymer-polymer surfaces. He argues that diffusion processes often lead to fractal interfaces. Although the concentration profile varies smoothly with the dimension of depth, the interface, considered in two or three dimensions is extremely rough [72]. Theoretical predictions, supported by practical measurements, suggest that the two-dimensional profile through such a surface is a self-similar fractal, that is one which appears similar at all scales of magnification. Interfaces of this kind can occur in polymer-polymer and in polymer-metal systems. 

Surface composition and morphology of copolymeric systems and blends are usually studied by contact angle (wettability) and surface tension measurements and more recently by x-ray photoelectron spectroscopy (XPS or ESCA). Other techniques that are also used include surface sensitive FT-IR (e.g., Attenuated Total Reflectance, ATR, and Diffuse Reflectance, DR) and EDAX. Due to the nature of each of these techniques, they provide information on varying surface thicknesses, ranging from 5 to 50 A (contact angle and ESCA) to 20,000-30,000 A (ATR-IR and EDAX). Therefore, they can be used together to complement each other in studying the depth profiles of polymer surfaces. 

FIGURE 31.9 Change in the peel strength and radiation dose of ethylene-propylene-diene monomer (EPDM)/EPDM joint [Eo/y Eo/yl EPDM/natural mbber (NR)/EPDM joint [Eo/y NR Eo/yl and EPDM/Al joint [Eo/y Al]. (From Sen Majumder, P. and Bhowmick, A.K., in Polymer Surface Modification Relevance to Adhesion, Vol. It, Mittal, K.L., Ed., VSP, Utrecht, The Netherlands, 2000,425. With permission.)... 

Tanaka, M. and Sackmann, E. (2005) Polymer-supported membranes as models of the cell surface. Nature, 437, 656-663. 

A PP sample after ozonization in the presence of UV-irradiation becomes brittle after 8 hrs of exposure, whereas the same effect in ozone is noticeable after 50-60 hours.Degradation of polymer chain occurs as a result of decomposition of peroxy radicals. The oxidation rapidly reaches saturation, suggesting the surface nature of ozone and atomic oxygen against of PP as a consequence of limited diffusion of both oxygen species into the polymer. Ozone reacts with PP mainly on the surface since the reaction rate and the concentration of intermediate peroxy radicals are proportional to the surface area and not the weight of the polymer. It has been found that polyethylene is attacked only to a depth of 5-7 microns (45). 

Many polymer items are designed specifically to make contact with other materials. Where surface contact is concerned, two key properties are coefficient of friction and abrasion resistance. Polymers used in such applications include ultra high molecular weight polyethylene, polyacctal, fluorinated polymers, and natural and synthetic rubbers. Examples that we routinely come across include furniture upholstery, bushings and gears in office equipment, and bicycle tires. Industrial uses include the outer cover of electrical cables, and pipes that convey abrasive liquids such as slurries and powders. 

The effects of calcium on polymer-solvent and polymer-surface interactions are dependent on polymer ionicity a maximum intrinsic viscosity and a minimum adsorption density as a function of polymer ionicity are obtained. For xanthan, on the other hand, no influence of specific polymer-calcium interaction is detected either on solution or on adsorption properties, and the increase in adsorption due to calcium addition is mainly due to reduction in electrostatic repulsion. The maximum adsorption density of xanthan is also found to be independent of the nature of the adsorbent surface, and the value is close to that calculated for a closely-packed monolayer of aligned molecules. 

It is believed that polymer surface fluorination proceeds via a free radical mechanism, where fluorine abstracts hydrogen atoms from the hydrocarbon, and fluorine atoms are substituted.11 Of course, the precise conditions depend on the nature of the polymer in question and the surface properties required. 

Fig. 19. SEM left a calcite-imprinted polymer surface after HCl/MeOH wash right nucleation of calcite at the imprinted polymer surface in the presence of CaCl2 (1.0 mmol/1), Na2C03 (0.8 mmol/1). Reprinted with permission from D Souza SM, Alexander C, Carr SW, Waller AM, Whitcombe MJ,Vulfson EN (1999) Nature 398 312. Copyright 1999 Macmillan Magazines Ltd... 

The characterization of the surface chemistry of the modified polymer is one step in understanding the mechanism for cells adhesion. The next crucial step is to determine the nature and extent of chemical interactions between the overlayer of interest and the modified polymer surface. This step presents a challenge because cmrently there are no techniques available with the sensitivity to characterize chemical interactions for an atomically thin buried interface. Several approaches have been used to analyze buried interfaces. Ion sputter depth profiling (typically done with Ar ions) in conjunction with XPS can be used to evaluate a buried interface for overlayers >10 nm [2]. 

J. Klein and P.R Luckham Long-Range Attractive Forces Between Two Mica Surfaces in an Aqueous Polymer Solution. Nature 308, 836 (1984). 

The adsorption experiments were carried out by quantifying each of proteins adsorbed on the material from mono-component protein solutions, from four-component protein solutions, and from plasma and diluted plasma. Adsorption profiles of protein were largely different, depending on the aforementioned experimental conditions. For instance, the behavior of any particular protein from diluted plasma varied in response to the extent of plasma dilution. Cooper s results are illustrated in Fig. 3, on fibrinogen adsorption onto five polymer surfaces. It is seen that the adsorption profiles are different one another, being influenced by the different nature of the polymer surfaces. The surface concentrations of adsorbed protein are mostly time-dependent, and maxima in the adsorption profiles were observed. This is interpreted in terms of replacement of adsorbed fibrinogen molecules by other proteins later in time (Vroman effect). Corresponding profiles were also presented for FN and VN. 

The only other considerations are weathering, color development, and perhaps long-term oxidation. These are considered unfortunate problems to be minimized by various formulation techniques. In an extreme case, we all recognize that polyurethanes can be fire hazards, and this too must be addressed by various formulation technologies. In a sense, the slight reactivity of polyurethanes is considered a problem. We hope to show that opportunities arise from using the natural reactivity of the polymer surface and by making the polymer reactive to the environment with which it comes into contact. 

Way back in 1968 Dr. Silver was working for 3M on pressure-sensitive adhesives. These are glues that bond instantly to a surface but can be removed without destroying that surface. Today we are very familiar with such products peel-off stickers are everywhere. In 1968, however, they were virtually unknown. Scientists did realize that certain polymers, like natural rubber, could be peeled off under the right conditions, but they were not ideal. So Silver went to work. He investigated various synthetic polymers and eventually came up with one that was a weak adhesive and could be pulled off a surface. The difficulty was that it would not always pull off cleanly, and Silver lost interest. 

After natural ageing, again an increase in the water contact angle, was observed. However, the values of the untreated polymer surface were never reached. 

---