The development of the dynamic glass transition in poly(n-alkyl methacrylate)s is investigated with broad-band dielectric spectroscopy in the frequency range from 10-4 to 109 Hz. The experimental data were analyzed by adjustment with one or a sum of two Havriliak Negami functions. Upon decreasing the temperature, the high-temperature relaxation (a) changes into the local β relaxation (Johari Goldstein mode), and the cooperative α relaxation sets in close to this aβ transition. For poly(n-butyl methacrylate) a separate onset (zero intensity) of the α process and a parallel course of both traces in the Arrhenius diagram were observed. The activation energy of the β process does not change in spite of the parallel development of the α process. On the other hand, for poly(ethyl methacrylate) the α onset is close to a bend in the local process, i.e., the activation energy of the latter changes after the α onset. In both materials the intensity of the α process linearly increases with falling temperatures but with different intensity. Several scenarios for the αβ-splitting region are suggested.
Stability of the dielectric parameters in the R splitting region against methodical variations is demonstrated. The Williams product ansatz for correlation functions and an additive ansatz for dielectric functions are compared for poly(ethyl methacrylate). Both evaluation methods give a diminishing R intensity with increasing temperature, and a separate trace for the R relaxation different from both the secondary relaxation below and the high-temperature a process above the crossover. Furthermore, measurements on different poly(n-butyl methacrylate) samples and evaluation results of different experimentalists are compared. The intensity onset of the cooperative R relaxation, starting from zero at a characteristic temperature T on in the crossover region, and the parallel course of R and relaxations below Ton, separated by about one frequency decade in an Arrhenius diagram, remain stable against measurement and evaluation variations. A. IntroductionThe dynamic glass transition (main transition or, conventionally, R relaxation) in low-molecular-weight glass formers, network glasses, and amorphous polymeric materials is usually accompanied by different secondary relaxations ( , γ relaxations and so on). 1,2 Whereas the glass transition at low temperatures is assumed to be caused by the cooperative motion of many particles, the secondary relaxations are of more localized molecular origin (for instance, Johari-Goldstein or process). 3,4 This process is distinct from the fast relaxation process in the picosecond time scale as described by the mode-coupling theory, 5 and distinct from the scattering effects at the boson peak. 6 The temperature dependence of characteristic relaxation times τ ) 1/ω max for the different processes can be visualized in an Arrhenius or activation diagram (log τ as a function of 1/T, ω max is the frequency of the maximum dynamic loss susceptibility, ′′(ω) here). The main transition is characterized by a curved trace, in particular for fragile glass formers, 7 whereas the traces of the secondary relaxations usually are straight lines.With increasing temperature and frequency the main transition and the trace will usually approach each other. 1 This crossover region, 8 called the R splitting region here, is of great importance for understanding the development of the glass transition below the crossover and the relation between both relaxation processes. To distinguish the qualitatively different relaxation processes of the main transition above and below the crossover we call the low-temperature part R and the high-temperature part a. 9 The details of the R splitting region were investigated in poly(n-alkyl methacrylate)s by means of broadband dielectric spectroscopy. 10 Supposing additivity of the R and compliances, an intensity onset of the cooperative R process, starting from zero at a characteristic onset temperature T on , was observed in all examples. For poly(n-butyl methacrylate) the traces of the developing R relaxation and the relaxation are parallel in the crossover region, separate...
The main transition of amorphous polymers is analyzed with respect to a fine structure by means of new experimental dynamic shear, dielectric, and heat capacity data for the following polymers: poly(n-alkyl methacrylate)s with alkyl = methyl, ethyl, propyl, butyl, and hexyl, polystyrene, poly(vinyl acetate), a series of weakly vulcanized natural rubbers, a series of butyl rubbers with different carbon black content, polyisobutylene, and bromobutyl rubber. The components of the fine structure are assumed to be a proper glass transition at short times, followed by a confined flow zone, and, at large times, a hindering zone caused by entanglements at large times. Two lengths are assumed to correspond to the first and third components, respectively, the characteristic length to the proper glass transition and the entanglement spacing to the hindering zone. The confined flow will be described by a dispersion law (general scaling) across the main transition. The characteristic length of the glass transition for the poly(n-alkyl methacrylate)sonly of order 1 nm as determined by calorimetryis confirmed by backscaling from the entanglement spacing by means of a Rouse dispersion law for shear. The fate of the Rouse modes below the αβ splitting of the glass transition is discussed for the other amorphous polymers. Finally, a speculative molecular picture of the different modes in the main transition is described. The new element is a low-viscosity longitudinal motion of individual chain parts in the confined flow zone. A simple rheological model for the confined flow is also presented.
An optical technique for the parallel manipulation of nanoscale structures with molecular resolution is presented. Bioconjugated metal nanoparticles are thereby positioned at the location of interest, such as, e.g., certain DNA sequences along metaphase chromosomes, prior to pulsed laser light irradiation of the whole sample. The nanoparticles are designed to absorb the introduced energy highly efficiently, in that way acting as nanoantenna. As result of the interaction, structural changes of the sample with subwavelength dimensions and nanoscale precision are observed at the location of the particles. The process leading to the nanolocalized destruction is caused by particle ablation as well as thermal damage of the surrounding material.
Dynamic dielectric and mechanical responses in the splitting region of PnBMA are analysed with the help of two Havriliak-Negami-function fits. The alpha and beta processes in the Arrhenius diagram are parallel to each other over a wide temperature range, and do not merge.
The manipulation of polymers and biological molecules or the control of chemical reactions on a nanometer scale by means of laser pulses shows great promise for applications in modern nanotechnology, biotechnology, molecular medicine or chemistry. A controllable, parallel, highly efficient and very local heat conversion of the incident laser light into metal nanoparticles without ablation or fragmentation provides the means for a tool like a 'nanoreactor', a 'nanowelder', a 'nanocrystallizer' or a 'nanodesorber'. In this paper we explain theoretically and show experimentally the interaction of laser radiation with gold nanoparticles on a polymethylmethacrylate (PMMA) layer (one-photon excitation) by means of different laser pulse lengths, wavelengths and pulse repetition rates. To the best of our knowledge this is the first report showing the possibility of highly local (in a 40 nm range) regulated heat insertion into the nanoparticle and its surroundings without ablation of the gold nanoparticles. In an earlier paper we showed that near-infrared femtosecond irradiation can cut labeled DNA sequences in metaphase chromosomes below the diffraction-limited spot size. Now, we use gold as well as silver-enhanced gold nanoparticles on DNA (also within chromosomes) as energy coupling objects for femtosecond laser irradiation with single-and two-photon excitation. We show the results of highly localized destruction effects on DNA that occur only nearby the nanoparticles.
Driven by the demand for ongoing integration and increased complexity of today's microelectronic circuits, smaller and smaller structures need to be fabricated with a high throughput. In contrast to serial nanofabrication techniques, based, e.g., on electron beam or scanning probe methods, optical methods allow a parallel approach and thus a high throughput. However, they rarely reach the desired resolution. One example is plasmon lithography, which is limited by the utilized plasmonic metal structures. Here we show a new approach extending plasmonic lithography with the potential for a highly parallel nanofabrication with a higher level of complexity based on nanoantenna effects combined with molecular nanowires. Thereby femtosecond laser pulse light is converted by Ag nanoparticles into a high plasmonic excitation guided along attached DNA structures. An underlying poly(methyl methacrylate) (PMMA) layer acting as an electron-sensitive resist is so structured along the former DNA position. This apparently DNA-guided effect leads to nanometer grooves reaching even micrometers away from the excited nanoparticle, representing a novel effect of long-range excitation transfer along DNA nanowires.
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