Dynamics Of PAMAM Dendrimers As Reveal By Dielectric Relaxation Spectroscopy

In this thesis,we utilize Broadband dielectric relaxation spectroscopy(BDS)to investigate the dynamic properties of poly(amidoamine)PAMAM,a commercially available dendrimer,from generation 0 to 4.The dielectric properties of PAMAM dendrimers with the same framework but different functional groups at the surface and different generation numbers are also studied by using BDS.To investigate their dynamics,we use differential scanning calorimetry(DSC)first,followed by dielectric relaxation spectroscopy.Dielectric relaxation spectroscopy,also known as impedance spectroscopy,is a widely used spectroscopic tool for evaluating different polymers.It determines the response of a polymer to an applied electromagnetic wave(typically at RF and MW frequencies)in terms of frequency-dependent complex relative permittivity?*,which has a real part(dielectric constant?')denoting energy storage and an imaginary part(dielectric loss?'')denoting energy dissipation.BDS refers to the measurement of a material's responses to an applied electromagnetic wave in terms of frequency-dependent DPs,such as relative complex permittivity and complex conductivity.Because a sufficiently weak electromagnetic field is applied to a matter in most cases to achieve a linear response with the applied field,BDS is essentially non-invasive.BDS is an ideal in-situ and real-time characterizations technique because of its many attributes,including swift measurement,affordable instrumentation,comparatively easy sample preparation,and incredibly broad frequency and temperature range coverage.In this thesis,we use various parameters such as temperature and relaxation time to evaluate the dielectric properties and dynamics of PAMAM dendrimers of the first five generations having the same framework and same functional group(NH₂),i.e.generation 0through 4.PAMAM dendrimers with the same backbone but different functional groups and generation numbers(-NH₂,-OH,-COOH,-COOCH_3,and–COONa)are also investigated.Except for the PAMAM dendrimer with–COONa functional group,which has a temperature range of–140 ⁰C to 200 ⁰C,the dielectric relaxation spectroscopy(BDS)approach was used to study the molecular dielectric relaxation behavior patterns in the frequency range of(10^-1 to 10⁷ Hz)and temperature range of(-140 ⁰C to 100 ⁰C).Overall,five relaxations were observed in the frequency range mentioned,one non-symmetric i.e.?relaxation governed by the Vogel-Fulcher-Tammann(VFT)method,and four types of symmetric relaxations governed by the Arrhenius law,namely ultra-low frequency range,?,?,and?and.The Logarithmic method was used to further stimulate these relaxation behaviors,and their relaxation characteristics were accurately summarized.It was noted that glass transition temperature(T_g)and fragility increases with the increasing temperature and generation of dendrimers,which might be due to the increasing molecular weight and distribution of the electronic cloud(functional groups)at the terminals.Furthermore,an increase in time scale was observed concerning the temperature which might be due to the contribution of hydrogen bonding between the dendrimers.The goal of this research is to figure out how to ascertain the dielectric relaxation behaviors of PAMAM dendrimers practically.The findings of this study will aid in a better understanding of PAMAM dendrimer molecular dynamics,structure,glass formation,and fragility.