Relaxation dynamic scattering

Despite the high energy resolution and extreme surface sensitivity only few studies on the dynamics of adsorbate covered surfaces have been performed so far by He scattering " However, the vibrational states of adsorbates are relevant for most dynamical surface processes like scattering, accommodation, desorption, or diffusion, and therefore, their nature and relaxation dynamics deserve more attention. 

Fig. 53. Computed decay of the dynamic scattering function for a rather stiff dumbbell according to Ref.215). The rotatory diffusion coefficient is 0, qL = 2, a = L/50, r = 0/2500. L = length of the dumbbell, a2 = mean square amplitude of the bond stretching, r = a2/4 D stretching relaxation time321 ...

Dynamic scattering can also provide information about relaxation modes of polymers at higher values of the wavevector q ( 7 >1). Equation (8.164) can be generalized to higher wavevectors and to semi-dilute and concentrated solutions by noticing that the decay of the... 

Zhou X. and Hsiang T. Y. (1990), Monte-Carlo determination of femtosecond dynamics of hot-carrier relaxation and scattering processes in bulk GaAs , J. Appl. Phys. 67,7399-7403. 

Dynamic scattering occurs due to the relaxation of the concentration fluctuations of polymer segments with the scale commensurable with (see subsection 2.1.2). So, the relative contribution of the diffusion mobility of the macromolecules and their internal modes of motion depends on the wave vector q. 

Tanaka et al. (1973), Munch et al. (1976) have shown that in cro.sslinked gels, the dynamic scattering spectrum has the Lorentzian form w ith the relaxation time... 

BordaUo HN, Zakharov BA, Boldyreva EV, Johnson MR, Koza MM, Seydel T, Fischer J (2012) Application of incoherent inelastic neutron scattering in pharmaceutical analysis relaxation dynamics in phenacetin. Mol Pharm 9 2434-2441 Bptker JP, Karmwar P, Strachan CJ, Cornett C, Tian F, Zujovic Z, Rantanen J, Rades T (2011) Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pairwise distribution functions. Int J Pharm 417 112-119 Boutonnet-Fagegaltier N, Menegotto J, Lamure A, Duplaa H, Caron A, Lacabanne C, Bauer M (2002) Molecular mobihty study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectrometry. J Pharm Sci 91 1548-1560 Bras AR, Noronha JP, Antunes AMM, Cardoso MM, Schdnhals A, Affouard Fdr, Dionfsio M, Correia NIT (2008) Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy. J Phys Chem B 112 11087-11099... 

The relaxation time To of the director is much longer and, consequently, is a limiting step in the relaxation process of the dynamic scattering caused... 

Dynamic scattering techniques probe the relaxation of fluctuations at a scale determined by the instrumental wave number q. In particular, the relaxation time of concentration fluctuations is found to be... 

It is well known that the a-process has a wide distribution of the relaxation time and hence there is a possibility that the E-process is a tail of the a-process. Due to the wide distribution of the relaxation time the intermediate scattering function due to the a-process is described by a stretched exponential function [exp(-(t/T) ) 0< < ]. In order to check this possibility, we fitted a dynamic scattering law, Sjjn(Q>(o)> derived from the Havriliak-Negami (HN) function (see Eqs. 32 and 33) to the observed S(Q,co). The HN function (co) and SjjN(Q.ro) are given by... 

This is too fast for nematics operated in dynamic scattering, but it is usable in electrically controlled birefringence (ECB). In ECB the nematic can respond to short duration pulses if the repetition frequency is high enough. The liquid crystal can summate a series of small excitations. If r is the pulse duration and T the repetition period, the optical retardation does not depend on r or T if these quantities are larger than the molecule relaxation time. The only important parameter is r/T. 

The smaller number of techniques used for the study of polymer sohds are broad band dielectric relaxation, dynamic mechanical thermal analysis, smaU angle inelastic neutron scattering and NMR, which together span a frequency range of 10 to 10 Hz. So, they can be used to study aU the correlation frequencies that characterise the motions of interest. 

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