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An investigation was carried out by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) on the dynamics of aqueous solutions of deoxyribonucleic acid (DNA). Novel information is generated and presented through our use of wide temperature and frequency range in DRS and DMS measurements. Two relaxation processes were detected at temperatures below 273 K. The higher frequency, Debye-like process has an activation energy of 27 kJ/mol and is assigned to the bound water around DNA molecules. The lower frequency process is of the Cole−Cole type and has an activation energy of 55 kJ/mol, the same as that of pure ice. In the higher temperature range, encompassing the physiological condition, conductivity dominates the dielectric response. A pronounced peak in the dielectric modulus spectrum is observed, and its molecular origin is found to lie in the migration of counterions along the DNA surface. Using Manning's model, it was calculated that the subunit length over which counterions fluctuate increases from 70 nm at a concentration of 2 mg/mL to 153 nm at a concentration of 0.125 mg/mL. The results of DMS measurements of aqueous solutions of calf thymus DNA reveal a G‘/G‘ ‘ crossover point whose frequency (ωC) scales with concentration as ωC ~ CDNA^-2.4. The implication is that the DNA molecules behave as semiflexible polymers in aqueous solution. The temperature dependence of ωC indicates that the breakup of the DNA base pairs and the chain melting begin at a temperature as low as 50 °C.

An investigation was carried out on the effect of molecular architecture on the dynamics of multigraft (MG) copolymers of polyisoprene (PI) and polystyrene (PS). MG copolymers with regularly spaced multiple grafts with trifunctional (combs), tetrafunctional (centipedes), and hexafunctional (barbwires) branch points were synthesized by anionic polymerization and studied by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS). The PI precursors were characterized by the presence of segmental and normal mode processes. The temperature dependence of the dielectric relaxation time for the segmental (τS) and normal mode (τN) process was of the Vogel−Fulcher−Tammann (VFT) type. In the entangled regime τN scales with M^4.0. The major findings for the MG copolymers are as follows:  (1) all MG copolymers are characterized by the presence of segmental and normal mode relaxation; (2) τS is independent of molecular weight and architecture; (3) τN is slower in a MG copolymer than in its PI precursor; (4) τN in a MG copolymer of a given architecture is not a function of the overall molecular weight or the number of branch points; (5) the difference between the normal mode relaxation time for a MG copolymer, τN(PIPS), and its PI precursor, τN(PI), defined as ΔτN = τN(PIPS) − τN(PI), depends strongly on the molecular weight of the PS graft (MPS). An explanation was offered for the reasons underlying the observed slowdown of the normal mode relaxation in MG copolymers vis-à-vis their PI precursors.

The frequency-dependent shear moduli were measured over a range of temperature for polyisoprene (PI, M = 22 000 and 78 000), poly(vinylethylene) (PVE, M = 10 000 and 120 000), and their blends. The longest relaxation times of each component in the blends were extracted by a modified Tsenoglou mixing rule, and converted to monomeric friction factors via the reptation model. Dielectric relaxation and pulsed field gradient NMR were used to follow the terminal relaxation and diffusion, respectively, of a low molecular weight PI (M = 1300) in blends with perdeuterated PVE (M = 2300), for a range of temperature and composition. In this case monomeric friction factors were extracted via the Rouse model. The friction factors for PI via all three techniques agreed quantitatively, and the friction factors for both components were independent of molecular weight. Segmental dynamics of each component in PI/PVE blends by NMR methods, reported in the literature, could be compared directly with the terminal relaxation data. In all cases, the segmental and terminal dynamics exhibited equivalent dependences on temperature and composition. The predictions of the model of Lodge and McLeish were compared to the combined data, by calculating component self-concentrations and effective glass transition temperatures using a single temperature-independent length scale. As anticipated in the original model, this length scale is close to the Kuhn length of the particular component. In the case of PI, the model provides a quantitative description over the entire composition and temperature range studied. For PVE the agreement is not as quantitative, but it is still quite satisfactory.

An investigation was conducted of segmental and normal mode dynamics during cross-linking of reactive systems where one of the components exhibits, in addition to the transverse dipole moment (μ^⊥) component that gives rise to the segmental α process, a persistent cumulative dipole moment (μ^∥) along the chain contour that can be relaxed via the normal mode process. The systems studied were composed of an amine-terminated linear or three-arm star poly(propylene oxide), which contains both μ^⊥ and μ^∥, and a bifunctional epoxy prepolymer. The kinetics of network formation were evaluated by Fourier transform near-infrared spectroscopy (NIR), and the dynamics were investigated by broad-band dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS). The dynamics of networks containing linear and star chains were similar but not identical. The average relaxation time for segmental (τS) and normal mode (τN) increases in the course of network formation, but the distance between τS and τN varies little and the Tg-scaled fragility remains unchanged. The spectra become thermodielectrically complex following the onset of reactions and broaden in the course of cure. Segmental and normal mode relaxations overlap increasingly during cure but, interestingly, retain their identities. There is a decrease in the dielectric relaxation strength for the segmental process (ΔεS) and a simultaneous (unexpected) increase in the dielectric relaxation strength for the normal mode process (ΔεN). Before gelation, the DMS response was characterized by segmental and terminal relaxation zone. The gel point was observed at a conversion above that predicted by the gelation theory, and an explanation was put forward.

An investigation was carried out of the molecular interactions and local relaxation dynamics in glassy polymer networks exposed to moisture. Stoichiometric and off-stoichiometric mixtures of the diglycidyl ether of bisphenol A (DGEBA) and diethylene triamine (DETA) were prepared, cured, and investigated. The physical and the chemical nature of the interactions between the network and the absorbed moisture were studied by broadband dielectric relaxation spectroscopy (DRS), Fourier transform near-infrared (FT-NIR) spectroscopy, and molecular simulations. Dry networks are characterized by two Arrhenius-like local relaxations:  the β process, associated with hydroxyl groups, and the γ process, associated with primary and secondary amine, and glycidyl ether groups. Absorbed water interacts with the network and affects the dynamics of β and γ processes. FT-NIR spectra reveal the presence of three forms of water molecules, differing in the number of hydrogen atoms (0, 1, or 2) that participate in hydrogen bonds. The relative ratio of each form to the total absorbed water was calculated from the NIR data and from molecular simulations. An excellent agreement between those two techniques was observed.

An investigation was carried out of the normal and segmental dynamics of poly(propylene oxide) (PPO) chains with (1) symmetrical dipole inversion and (2) three-arm star configuration. PPO chains exhibit, in addition to the transverse dipole moment component (μ^⊥) that gives rise to segmental (α) process, a persistent cumulative dipole moment along the chain contour (μ^∥) that can be relaxed via the normal mode (αN) process. Data were generated by broad-band dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS), and the findings were contrasted. In comparison with the previous studies of PPO dynamics, our DRS and DMS results were generated over a broader range of frequency and temperature and on samples of a wider range of molecular architecture (molecular weight, type, and functionality of end group). Segmental and normal mode spectra were thermodielectrically simple (with the KWW β parameter of ca. 0.51). The average relaxation times for the segmental mode (τS) from DRS and DMS were in excellent agreement. A direct comparison of the normal mode relaxation times (τN) obtained from DRS and DMS data had to account for the longest viscoelastic relaxation time (τN1DMS) of the Rouse chain being one-half the longest dielectric relaxation time (τN1DRS) and twice the second dielectric normal mode relaxation time (τN2DRS), which is experimentally measured. We observed excellent agreement between (1) our DRS and DMS data, (2) our data and the results of other groups, and (3) our data and the prediction of the Rouse model for MW less than 12 000 g/mol. The molecular weight dependence of τN1DMS at 273 K is characterized by an exponent of 2, in perfect agreement with τN2DRS.

An investigation was carried out of the molecular dynamics of poly(l-lactic acid) before, during, and after crystallization. Experimental results were generated over a wide range of temperature and frequency by broad-band dielectric relaxation spectroscopy (DRS). An interesting finding is that the average relaxation time (defined as τ = ¹/2πfmax, where fmax is the frequency at maximum loss for the α process) does not vary with degree of crystallinity during melt and/or cold crystallization. Moreover, the temperature dependence of the average relaxation time for wholly amorphous and crystallized samples is well-described by a single Vogel−Fulcher−Tammann (VFT) functional form. The unchanged fragility suggests that the segmental dynamics are not sensitive to the different degree of crystallinity, implying that the relaxing segments are smaller than the thickness of the amorphous layers between lamellae. Apparently, the distance between lamellae is greater than the length of the primitive segment and the characteristic size of the cooperatively rearranging domain; the length scale of the α process is thence put at less than 4 nm.

A liquid crystal monomer (LCM) was synthesized and attached as a side chain to a siloxane polymer (SCLCP). The molecular dynamics of LCM and SCLCP were investigated by broad-band dielectric relaxation spectroscopy (DRS) over 10 decades of frequency. The surface treatment of the electrodes was found to have a pronounced effect on the macroscopic alignment and dynamics. In the isotropic state the relaxations in LCM and SCLCP are well-described by the Kohlrausch−Williams−Watts (KWW) functional form. In the LC state, the overall dielectric response is a weighted sum of two dispersions that depend on the macroscopic alignment. The hometropic (H) alignment is dominated by the (slower) δ process, while the planar (P) alignment is dominated by the (faster) αm process. Both processes are symmetric and can be described by Cole−Cole (CC) or Fuoss−Kirkwood (FK) functional forms. The δ process governs the dynamics in the SCLCP near the glass transition, similar to the segmental α process in non-LC glass formers. Excellent agreement was observed with the various aspects of the seminal work by Attard and Williams.

We have investigated a set of small molecules, which, in terms of chemical groups and overall molecular architecture, are representative of several of the more complex epoxide/amine network-forming systems. The static and dynamic dielectric relaxation properties of selected model compounds are obtained and discussed. The static properties are of interest for their relation to the fundamental material property, the dipole moment. From this relation, the potential for the determination of the chemical composition of reactive mixtures via an additivity of group dipole moments is explored. Dipole dynamics of the model compounds are determined and are related to cooperative molecular and submolecular motions in these simple molecules and it is shown how these findings may be extended to complex polymer networks composed of chemically similar moieties.

Molecular dynamics and morphology in the blends of a network-forming reactive polymer and an amphiphilic block copolymer were examined as a function of the advancement of chemical reactions. In the blends containing a triblock copolymer, both microscopic (domains of the order of micrometers) and nanoscopic (domains of the order of nanometers) phase separations were observed during network formation. Interestingly, only nanoscopic phase separation was found in the blends containing a diblock copolymer. The shape and the origin of these nanoscopic features were investigated by atomic force microscopy and were found to be a function of blend composition. A concept was advanced of the three-phase nanostructured morphology that begins to form with self-assembly of one block and continues to develop during network formation in the postassembly stage. The changes in relaxation dynamics that accompany network formation were monitored by broad-band dielectric relaxation spectroscopy (DRS) and were shown to represent a signature of the morphological state of the blend. The ability of DRS to identify and deconvolute various relaxation processes during network formation and phase separation is noteworthy and should be exploited as means of monitoring and controlling the development of nanostructured morphology in these complex systems.

Molecular dynamics via broad-band dielectric relaxation spectroscopy (DRS) are obtained on a class 3 network-forming system:  a generic cyanate ester resin. The potential for in-situ monitoring of the network-forming reaction is explored. The segmental dynamics of the growing network are investigated, and a hitherto unknown secondary relaxation process, β*, is found. This relaxation is distinctly different from the Johari−Goldstein slow β process. Model compounds and conformational strain analysis are used to elucidate the β* relaxation molecular mechanism. The α process in selected cyanate networks was analyzed with the Adam−Gibbs thermodynamics-based relations (AG model). The AG model provides a link between the relaxation time of a cooperatively rearranging domain (CRD) and configurational entropy. The model is explored via DRS and calorimetrically for various network structures. A good agreement is found between independent quantities derived from both techniques when examined in the AG framework. These results lend support to the CRD concept used in the AG model and, more generally, toward the establishment of the heterogeneous view of relaxations in glass-formers.

A comprehensive investigation of the reorientational dynamics of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends was carried out. Dielectric relaxation spectroscopy (DRS) was performed over 11 decades of frequency and over a wide range of temperature on wholly amorphous, crystalline, and crystallizing blends of varying composition. The range of experimental conditions and compositional variables far exceeded those employed by previous investigators, enabling us to formulate a comprehensive view of the dynamics in these systems. A number of relaxation processes were detected, and their origins, temperature dependence, composition dependence, and spectral characteristics were established. Three α-type processes were observed:  the αa process, associated with relaxations of all amorphous PVDF segments (not only within the crystalline−amorphous interphase); the αm process, which encompasses several relaxation processes and scales with blend composition; and the αc process, attributed to relaxations within the crystalline phase. With decreasing temperature the αa process in the blends undergoes a crossover to a localized βa process, in a manner different from the αβ splitting observed in many molecular and polymeric glass formers. An explanation of the underlying physics was offered within the framework of an interplay between the physical dimension of various nanoscopic regions in the blend and the characteristic length scale for cooperative relaxation. The αaβa crossover was shown to be a consequence of the confinement imposed on the amorphous PVDF segments by more rigid PMMA segments and the PVDF crystals.

Dipole dynamics of a series of thermotropic liquid crystalline (LC) epoxy prepolymers and an LC epoxy/amine network were studied by broad-band dielectric relaxation spectroscopy (DRS) over a wide range of frequency and temperature. Two relaxation processes were observed in the prepolymers below the melting point:  the β process, associated with the rotational motions of the LC rigid rods about their molecular axis, and the γ process, whose origin lies primarily in the localized motions of the terminal group. The α process, associated with the segmental motions, emerges as a low-intensity process above the calorimetric glass transition and quickly shifts into the gigahertz frequency range with increasing temperature. The δ process, associated with the end-over-end motions in the mesophase, is largely absent because of a negligible longitudinal dipole moment in these LC epoxy molecules. An in-situ investigation of the formation of an LC epoxy/amine network was conducted by DRS and polarized optical microscopy (POM). The initial stage of cure in the mesophase was characterized by the formation of nematic droplets, which quickly coalesce to form larger structures. An interesting observation was the spontaneous formation and the subsequent change of homeotropic to planar orientation during cure&sbd;a trend analogous to that observed by X-ray diffraction. Three relaxations characterize the dynamics of cured networks:  the α process due to segmental motions in the cross-linked network, the LC β process also observed in neat prepolymers, and the βOH process, associated with the localized motions of (primarily) hydroxyl groups.

Molecular dynamics of network-forming reactive polymers were examined as a function of the advancement of chemical reaction as the materials structure undergoes a transition from liquid to amorphous solid. The accompanying changes in the segmental relaxation time (α process) are a signature of the materials state (within the liquid to amorphous solid spectrum of physical properties). Both broad-band dielectric relaxation spectroscopy (DRS), which probes the α process via dipolar reorientational mobility, and dynamic light scattering (DLS), which probes the α process via density fluctuations, were used to monitor the system under reaction conditions in the reaction bath (to our knowledge, the first study of its kind). An excellent agreement was found between DRS and DLS for the α process characteristic parameters:  relaxation time and KWW, the stretched exponential parameter (characterizing the relaxation breadth). That dipole dynamics exhibit the same α relaxation characteristics as time dependent density fluctuations, suggests that the rotational motion observed in a DRS measurement is directly controlled by the behavior of the density domains. It was concluded that the broadening of the α process is due to a general phenomenon:  the micro/nanoscale heterogeneous nature of glass formers. The results of the study are discussed in terms of cooperative and local relaxation modes in the growing network.

The segmental dynamics of PMPS chains are determined in the bulk liquid and cross-linked networks of varying cross-link density by broad-band dielectric relaxation spectroscopy. A large fragility index [τ(Tg*/T) dependence], F1/2 = 0.77, is found, independent of cross-link density, molecular weight, and Tg. Also independent of the above variables is the relaxation shape (characterized by a KWW β parameter of 0.45). Since these parameters quantifying the α process in PMPS networks are insensitive to cross-linking, it is concluded that the length scale of cooperatively rearranging domains in PMPS networks is smaller than the distance between cross-links, i.e., less than 5 nm, in agreement with the current consensus. An argument based on the temperature dependence of the dielectric relaxation strength, dipole moment, and ensemble average chain configuration was advanced, suggesting that the high fragility of PMPS has an intramolecular origin.

An investigation was conducted to determine how the molecular architecture of prepolymers affects the dynamics of epoxy/amine networks at various stages of cross-linking. An epoxy prepolymer with a carbonyl group attached to the glycidyl ether moiety was utilized, in anticipation that the presence of the carbonyl group would have a specific affect on the interactions and dynamics in these networks. Experimental results were obtained in real time by simultaneous broad-band dielectric relaxation spectroscopy and near-infrared Fourier transform spectroscopy. An unusual increase in the relaxed (limiting low-frequency) dielectric constant was observed, and an explanation was offered in terms of an intramolecular hydrogen-bonded complex that co-involves carbonyl and hydroxyl groups. A pronounced change was also noted in the IR absorption of epoxy and carbonyl groups near the gel point and was assigned to specific dipolar interactions in the growing network. Frequency sweeps of reactive networks reveal initially the αβ process at high frequency (peak at ca. 2 GHz). With the advancement of reactions, however, α and β relaxations begin to separate out; α relaxation shifts gradually to lower frequency as the glass transition of the growing network increases, while β relaxation, because of its localized origin, is little affected by the network growth. An unusual form of thermodielectric complexity is observed in the relaxation spectrum for the α process. Finally, building upon an earlier study by Fournier et al. (Macromolecules 1996, 29, 7097), a correlation between molecular dynamics and chemical kinetics during network formation is reported.

The reorientational dynamics of dipoles in poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends were investigated by dielectric spectroscopy. Measurements were performed over a wide range of temperature and frequency, and previously unavailable results are reported. Various relaxation processes were identified and their locations assigned to the different morphological regions in PVDF, PMMA, and PVDF/PMMA blends. The development of a relaxation process associated with the imperfections in the crystalline phase was recorded both in pure PVDF and in crystalline blends. An amorphous interphase and a liquid-like amorphous phase are present in pure PVDF, but their relaxation dynamics are dielectrically indistinguishable, giving rise to a single non-Arrhenius relaxation mechanism. In the crystalline blends, however, the interphase is devoid of PMMA, and its relaxation dynamics are readily distinguishable from those of the PVDF/PMMA miscible phase. Interestingly, the relaxation dynamics in the interphase were found to vary as a function of blend composition. Since the relaxation processes are governed by cooperativity, an explanation of our findings is offered in terms of the interactive nature of the relaxation process.

An investigation was carried out on the mechanism and kinetics of cure of a two-component bismaleimide formulation, composed of 4,4‘-methylenebis[maleimidobenzene] and 2,2‘-diallylbisphenol A. In-situ real time study of the progress of reaction was conducted in the temperature range from 140 to 250 °C using remote fiber optic near-infrared spectroscopy. The obtained signal was clean, free of noise, and remarkably reproducible. The principal reaction observed was an alternating copolymerization involving maleimide and allyl double bonds. Maleimide homopolymerization was detected only in the initial stages of reaction at temperatures above 200 °C. The extent of self-condensation (or etherification) of hydroxyl groups on the allyl component, which leads to cross-linking, was observed to vary with reaction temperature, suggesting a path to tailor-making networks with desired morphology and physical/mechanical properties.

An investigation was carried out on the dynamics of polymer networks in the presence of a nonpolar solvent. The formulations studied were composed of a network-forming multifunctional epoxy−amine mixture and o-terphenyl as solvent. A number of formulations at various degrees of cross-linking and with different solvent concentration were prepared and investigated. Experimental results were generated by simultaneous broad-band dielectric relaxation spectroscopy and remote fiber-optic Fourier transform infrared spectroscopy. The emergence of specific interactions during the network formation was confirmed by FTIR and their effect on the dynamics of the α process was established. Dielectric data were analyzed in the time and frequency domain, and it was found that the network dynamics could be classified into three regimes as a function of degree of cure. The nature of relaxations in these three regimes was discussed. An interesting finding was that the dynamics were dominated by the short-range interactions in the vicinity of the gel point. The presence of solvent had a pronounced effect on the various aspects of dynamics, including the apparent activation energy for the α process, the distribution function, and the cooperative nature of relaxations.

An investigation was conducted to determine how the advancement of chemical reactions and the prepolymer molecular weight affect the reorientational dynamics and intermolecular cooperativity in model epoxy−amine systems. Experimental results were obtained by dielectric spectroscopy over a wide range of frequency and temperature. A strong effect of the progress of reaction on reorientational dynamics was noted and an explanation was put forward within the framework of the coupling theory, marking the first time this concept was applied to reactive systems. It was proposed that the molecular-level characteristics that govern the intermolecular cooperativity of reactive systems can be classified into two categories:  (1) molecular architecture, determined by molecular symmetry, rigidity, and steric hindrance, and (2) dielectric architecture, determined by the type and concentration of all dielectrically active species. Both molecular and dielectric architecture vary in the course of chemical reaction, and the overall direction in which the cooperativity shifts is governed by the interplay between these two phenomena.

An examination was carried out of the reorientational dynamics of dipoles during the network formation in multifunctional epoxy−amine systems. Experimental results were generated by simultaneous dielectric and Fourier transform infrared (FTIR) measurements. The observed changes in reorientational dynamics during the advancement of reactions were utilized to (1) describe the origin of the α relaxation during the network formation, (2) propose a methodology for the evaluation of the kinetics of network formation, and (3) advance an interpretation of network dynamics in terms of intermolecular cooperativity based on the interplay between molecular and dielectric architecture. Fragility or cooperativity plots proved most informative in relating intermolecular cooperativity to the molecular characteristics of the growing network.