Segmental Relaxation Behavior Of Core-forming Chains And Corona-forming Chains In Single Micelle

With the development of nanotechnology, three-dimensional?3D? confined polymers may be applied to many nanometer materials. As the closed relationship between molecular motion and the properties of macromolecular materials, the study on the dynamics of 3D confined polymer plays a vital role to exploit advanced polymer materials and develop emerging nanotechnology. Macromolecular spherical micelle is a self-assembly substance which has a core-shell structure with the diameters ranging from 10 to 100 nanometers. This special stucture provides a novel model to study the dynamics of 3D-confined polymer. People can prepare these spherical micelles by controlling their sizes and densities. In this paper, we use the polystyrene-b-poly?acrylicacid? or Poly?methyl methacrylate?-b-poly?acrylic acid? to self-assembly in dioxane/water mixed solvents to obtain sphere micelle solution.Utilizing the technology of atomic force microscope?AFM? to in-situ observe the height of single dry micelle with temperature, the segmental relaxation behavior of polystyrene?PS? chains in the core and poly?acrylic acid??PAA? chains in the corona could be obtanined. By this way, we study the effect of core density, polystyrene molecular weight and block length of poly?acrylic acid? on segmental relaxation of micellar core and corona. Major results are shown below:?1? We investigated the segmental relaxation behavior of polystyrene chains in the core and poly?acrylic acid? chains in the corona. With temperature elevating, the height of single micelle declines. It was found the height of single micelle with temperature shows two quick decline and the temperature range of the two height decline are 50⁷5? and 99¹03? respectively. Here we define the two beginning temperature of two height decline of single micelle as T _first onset and T_second^onset,respectively. By studying the mechanical property during the heating process on single micelle, we found that T _first onset belongs to the segmental relaxation of poly?acrylic acid? in micellar corona and T_second^onset belongs to the segmental relaxation of polystyrene in micellar core. By controlling the ralative ratio between water and dioxane, We prepared spherical micelles whose size and core density aredifferent. Then we studied the effect of core density on the segmental relaxation behavior of polystyrene chains in the core and poly?acrylic acid? chains in the corona.Results show that T _first onset rises with micellar density. However, the segment relaxation temperature(T_second^onset) of PS chains in micellar core is unchanged with temperature. The possible reason is attributed to that as the micellar density increases,single micelle size will shrink, which makes the PAA chains arrange more denser.While the free surface of micellar core is eliminated by the micellar corona, thus the segmental relaxatation temperature of PS chains in micellar core shows unchanged with temperature.?2? As PAA segment length fixed, the effect of PS molecular weight on the relaxation behavior of core / corona molecular chains has been studied. We discover that T _first^onset increases with core density,while ?T _first increases significantly with increasing molecular weight of PS chains. However, the micellar core segment relaxation temperature(T_second^onset) is not affected by the core density or molecular weight of PS chains, and is close to the PS bulk value. The effect of PS molecular weight on the segmental relaxation temperature of PAA chains in the corona is mainly due to the increasement of PS packing density. As we know, with PS molecular weight increasing from below entanglement molecular weight to above entanglement molecular weight of PS chains, the packing density of PS chains increases. Because of the covalent bond between the core and shell molecular chain, the micelle core?PS?density increases will limit the molecular motion of PAA chains in micellar corona.?3? By fixing the PS or PMMA segmental length, we study the effect of PAA length on the segmental relaxation of PAA chains in micellar corona. It was found that the increasement of PAA length leads to the increasement of T _first^onset under the same changement of core density. The possible reason is the increasement of the compactness of PAA chains in micellar corona. As PAA segmental length increases,the conformation of PAA molecular chains in micellar corona adopts the direction perpendicular to the surface of the micellar core. This streching conformation of PAA chains leads to more closer chain arrangement of PAA chains. In addition, micellar core size declines with PAA segmental length, and PAA chains arrange denser on themicellar core. The increasement of PAA packing density finally limits the motion of PAA chains. Possible reason is that with increasing PAA segmental length, the size of micellar core reduces, resulting in the increasement of micellar shell thickness. This leads to the increasement of the number of PAA molecular chain on unit surface area of micellar core. Finally, the PAA chains in the corona of micelle arrange more closely,resulting in restricting molecular motion of PAA shell.