Influence of Matrix Molecular Weight on a Brush - Like Surface Layer Formed by a Polymer Functionalised at Both Ends

Abstract

Deuteropolystyrene has been functionalised at each end by fluorosilane groups, the polymer obtained had a relative molar mass of 98 ×103. Thin films of this polymer mixed with unfunctionalised hydrogenous polystyrene have been prepared and the blends annealed to equilibrium at 413 K. The distribution of the end functionalised deuteropolymer was obtained by neutron reflectometry and a range of molecular weights of the hydrogenous polystyrene matrix has been used. In all cases the deutero polystyrene was preferentially located at the air-polymer interface to an extent which was far greater than that for unfunctionalised deutero polystyrene in the same hydrogenous matrices. From the near surface depth profiles obtained, the surface excess, surface volume fraction and thickness of the end functionalised deuteropolystyrene rich layer have been obtained as a function of the equilibrium concentration of end functionalised deuteropolystyrene. These parameters have been compared with the predictions of scaling theory for brush like layers of polymers attached to a surface. The surface layer thickness and average volume fraction of the surface layer display stretched wet brush behaviour which is not expected for end functionalised polymers on the basis of the molecular weights explored. The possibility that local grafting densities are significantly higher than the average value is discussed. The shape of the near surface depth profile has been fitted using a self consistent field theory using the “sticking energy” of the fluorosilane groups as the only adjustable parameter. Fits of reasonable quality were obtained and using this sticking energy the surface volume fractions and normalised surface excess parameters have been calculated and compared with those obtained experimentally. Good agreement between surface volume fractions is obtained, but the agreement between normalised surface excess values becomes increasingly worse as the relative molar mass of the hydrogenous matrix increases

Partitioning of a heterotelechelic polystyrene to separate interfaces of thin films

“…Influence of the fluorocarbon group and film thickness Figure 5 also shows the distribution of NDPS, the deutero polymer without the fluorocarbon end group, and it appears that the group has only a modest influence on the distribution. This is surprising because previous reports [8,12,31,32] show it to cause surface adsorption significantly in excess of that of the unmodified polymer.…”

“…Figures 8 and 9 show the volume fraction profiles obtained from the data fitting for bilayers with the lowest and highest molecular weight (H47 and H1700) hydrogenous polymers on top of the NDPSF m layer. For each composition profile the excess, z * , at each interface (where appropriate) was obtained using the relation (5) and the ellipsometric thickness [31] of each interfacial surface excess layer, L, from…”

“…Since the functional group responsible for the 'grafting' at each interface differs, this suggests that the free energy change on adsorption of the functional end to the surface is smaller for the fluorocarbon end at the air interface than the amine end at the silicon interface. We have previously shown that the surface excess for an end-adsorbed polymer can be quite well calculated using the self-consistent mean field approach developed by Shull [31,33]. This approach calculates a normalised surface excess, z * /R g , and provides a volume fraction distribution using a lattice model for the end attached / matrix polymer mixture adjacent to the adsorbing surface.…”

Influence of Architecture on Arm Dimensions and Interaction Parameters in Polybutadiene Star Polymers

“…In the main, polymer brushes are generally discussed when the molecules are attached to a planar surface and experimental studies in both bulk melts and dilute solutions have been reported. [37][38][39][40][41][42][43][44][45][46] Initially, the concept of stretching was confined to stars in dilute solution, but given the theoretical predictions, confirmed to some extent by experiment, of the stretched dry brush state, it is perhaps not surprising that we have observed stretching of the single labeled arm in the multiarm stars. Past experimental work has inferred the stretching of star arms from the global dimensions of the star polymers; 3,9,47 we have reported here a direct observation of this stretching for one arm of the star.…”

Novel evaluation method of neutron reflectivity data applied to stimulus-responsive polymer brushes

“…Beside the homogeneous layer model, Gaussian, exponential, and parabolic functions based on scaling theories have been used to analyze the reflectivity profiles. [25][26][27][28] Thermoresponsive polymer brushes are ideal samples for the proof-of-principle demonstration of our novel approach of modelling NR data. The fact that they can be stimulated into different hydration states while maintaining a fixed mass of polymer on the surface provides a self-consistent test of the method.…”