| Summary: | 博士 === 國立中央大學 === 化學工程研究所 === 89 === Abstract
The objective of this study is to research the application of crosslinked PDMS (polydimethylsiloxane) to contrast agent of NMRI (nuclear magnetic resonance imaging) for gastro-intestine. With emulsification and hydrosilylation, the crosslinked PDMS can be homogeneously dispersed in water to form colloidal solutions. The characters of these colloidal solutions are ascertained by FTIR spectra, MTT assay, NMR images, laser light scattering, steady-shear rheology, dynamic-shear rheology, NMR spectra, T1 relaxation and T2 relaxation. MTT assay indicates these colloidal solutions have low toxicity and NMR images illustrate they can intensify contrast in in-vitro gastrointestinal images. Regarding the NMR properties of the crosslinked PDMS colloidal solutions and the linear PDMS emulsions, the conventional equations for T1 relaxation and T2 relaxation (eqn.(2-4) and eqn.(2-5)) do not agree with some of experimental results such as T1 relaxation of -(CH2CH2O)- segments and T2 relaxation of crosslinked PDMS, water as well as -(CH2CH2O)- segments. For the rheology behaviors, there is a peculiar difference between the volume fraction (ψ) greater than and smaller than a critical value (ψc). These specific NMR properties and rheology behaviors are discussed in detail in chapters 4 and 5 respectively. However, ψ0.72 is more proper for the cosslinked PDMS colloidal solutions to consider the balance between comfort of oral administration and desired intensity of NMR signals.
With the assumption of geff0, Field-gradient NMR diffusometry[115] can be connected to T2 relaxation of polymers. A relation between T2 relaxation and Doi-Edwards tube-reptation model is further derived. The relation can be modeled by G(t)=exp[-(t/T2)n], in which n=1, 0.5 and 0.25 are for the regimes IV, III and II respectively. The different regimes of the tube-reptation model characterize the particular polymer dynamics, eg., the reptation and the wriggling dominate in the regimes IV and III individually. The model also implies a dynamic sequence from wriggling to reptation for the linear polymers with very high molecular weight. This work substantiates that 2.5x105 g/mole PDMS[70], 1.07x105 g/mole PE[82] and 1.2x105 g/mole PE[117] have T2 relaxation in agreement with G(t)=exp[-(t/T2)] as t>>td and with G(t)=exp[-(t/T2)0.5] as tR<<t<<td. These agreements support the dynamic sequence and give the relation feasibility for the tub-reptation model.
The T2 relaxation of the crosslonked PDMS coincides with G(t)=exp[-(t/T2)0.5], revealing the polymer chain has wriggling between crosslinked points. The liquid-like motion, wriggling, leads their NMR spectra are closed to a Lorentzian but not a Gaussian even though apparent feature of crosslinked PDMS is solid.
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