Diffusion Limited Aggregation of PMMA Stereocomplex in Thin Films
- PDF / 670,258 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 162 Views
DD4.3.1
Diffusion Limited Aggregation of PMMA Stereocomplex in Thin Films. Yves Grohens, Gilles Castelein1, Pascal Carriere1, Jiri Spevacek2 Laboratoire Polymères et Procédés, Université de Bretagne Sud, Centre de Recherche, rue St Maudé, BP 92116, 56321 Lorient Cedex, France 1 Institut de Chimie des Surfaces et Interfaces-CNRS, 15, rue J.Starcky, BP 2488, 68057, Mulhouse Cedex, France 2 Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 16206 Prague 6, Czech Republic.
ABSTRACT The nanoscale patterns formed by poly(methyl methacrylate) (PMMA) stereocomplexes at the surface of silicon wafers, glass and mica, were investigated by tapping mode atomic force microscopy (TM-AFM). The effects of the solvent nature, PMMA concentration, i/s-ratio (stoechimetry) and surface nature on the morphology of the stereocomplex thin layer at a surface were addressed. The aggregation phenomena are well described by the diffusion limited clustercluster aggregation model (DLA) and the fractal exponent D calculated. The i/s-ratio strongly influences the fractal exponent D which is equal to 1.35 for the 1:2 ratio is lower than for the other i:s ratios which are 1.46, 1.61, 1.82 for 1:1, 2:1 and 4:1 ratios, respectively. The low values of the fractal dimension D are indicative of a fast aggregation process and higher values of D correspond to a slow aggregation process.
INTRODUCTION Structures at surfaces at the nanometer scale are needed in many application fields such as microelectronic systems, filter technology or biosensors. Many routes have been envisaged to fabricate nano-patterned substrates such as copolymer crystallisation [1,2] LC polymers phase ordering [3] , microphase-separation [4] , and other self-association in amphiphilic polymers [5]. An original approach based on the properties of self-organisation of stereoregular polymers in certain solvents has been envisaged recently to vary the morphology of a thin laye [6,7]. Much efforts have been devoted over the past 40 years to the elucidation of the structure of stereocomplexes obtained from isotactic and syndiotactic poly(methyl methacrylate) (PMMA). Spevacek et al.[8] and Challa et al. [9] suggested a double stranded helix structure of the stereocomplex which is more consistent with the possible template polymerisation of stereoregular PMMA [10]. The physical gelation mechanism obtained for s-PMMA or PMMA stereocomplex suggests the physical network formed by intermolecular association of the helix structures in concentrated solutions [11]. The aim of this paper is to get better understanding of the mechanisms of the nano-scale aggregation of stereocomplexes at interacting surfaces. This system may also serve as a model for a better understanding in the mechanisms of proteins/surfactants aggregation near a surface.
DD4.3.2
EXPERIMENTAL DETAILS The stereoregular PMMA were supplied by Polymer Source. The solutions of stereocomplexes were prepared by mixing the two polymers in i:s = 1:2, 1:1, 2:1, 4:1 weight ratio in acetone. The concentratio
Data Loading...
