| In this thesis, the effects of molecular polarity on the diffusion rate of nonionic antistatic agents and the antistatic performances of poly(3-hexylthiophene) (P3HT) are investigated. It has been widely recognized that the diffusion rate of nonionic antistatic agents largely depends on antistatic molecular polarity, and the diffusion rate plays an important role in determining the antistatic performance and working life. However, studies on the polarity effect are not systematic nor enough, which is attributed to the limited experimental characterizing methods on molecular scale. In this context, molecular dynamic (MD)simulation is an effective route to explore molecule diffusion behaviors. Herein, we use LAMMPS as a MD simulation tool to investigate the polarity effects of nonionic antistatic molecules on their diffusion rates.A series of glycerin monostearate (GMS) derivatives are designed to explore the polarity effect, in which oxyethyl groups are incorporated in GMS molecule as polar parts to replace the ethyl groups, and the ester group in GMS acts as the demarcation point of polar and nonpolar parts. Then GMS and its five derivatives with varied lengths of oxyethyl groups are mixed within polypropylene (PP), respectively, to process the MD simulation. Our simulation results reveal that the polar part of the GMS derivatives tend to self-assemble into circle or helix shapes due to their chemical incompatibility with nonpolar groups, which is related to the length of polar groups. These self-assembled structures lead to the increase of molecular dynamic volume and thus reduce molecular diffusion rates. On the other hand, the diffusion rate of the GMS derivatives will be mainly determined by the polar part when their lengths are long enough, resulting in an increased diffusion rate since the flexibility of polar parts can promote molecular segmental motion. Therefore, the diffusion rate of GMS and its derivatives is observed to decrease with the increased length of polar part at 300K, and turns to increase from G-C2E3. Temperature influences the detailed value of diffusion rates, but not change this trend. At 350K, the diffusion rate also decrease at first and then increase with the increased length of polar part, but the minimum diffusion rate appears in G-C1E4. At 400K, the diffusion rate decrease at first and then stay almost the same from G-C3E2. At 350 K, G-C1E4 exhibits the lowest diffusion rate, while at 400 K, the diffusion rates of G-C3E2 to G-E5 are comparable.We also study aggregations of GMS at the surface of PP, and illustrate that GMS self-assemble into clusters with polar heads staying in the middle while nonpolar tails staying outside the clusters. In order to simulate the real environment, we add water layer in the simulation to study how GMS molecules are drawn to the surface of PP by moisture in air. We find that GMS molecules tend to move to the surface and reach a balance position.In addition, the antistatic performances of conjugated polymer P3HT are studied by characterizing the volume resistivity and surface resistivity of PP/P3HT composites. The results show that P3HT performs better than carbon blacks in reducing the surface resistivity. But similar to carbon blacks, P3HT suffers from changing the color of PP, which becomes purple with the addition of 0.5%wt P3HT. |
