Accurate New Method for Molecular Orientation Quantification Using Polarized Raman Spectroscopy

Richard‐Lacroix, Marie; Pellerin, Christian

doi:10.1021/ma400955u

Cited by 67 publications

(82 citation statements)

References 47 publications

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“…HDPE with low crystallinity exhibits larger 〈P 4 〉, which indicates a broader distribution of molecular orientation. These peculiar behaviors of 〈P 4 〉 are highlighted by considering the most probable distribution function 〈P 4 〉 mp [22,28,29,45]. In Fig.…”

Section: Resultsmentioning

confidence: 98%

“…For PE, the symmetric C-C stretching mode at 1130 cm −1 is relevant. The integrated intensities of the polarized spectra are expressed as [20,29,40,41]. Fig.…”

Section: Tablementioning

confidence: 99%

“…Because the C-C stretching vibration is strongly Raman active, microenvironments of the polymer chains are probed by the spectral shifts [26,27]. Polarized Raman spectroscopy gives not only a measure of the average orientation, which is obtained by the usual spectroscopies such as birefringence and IR dichrom, but also the orientation distribution function (ODF, N(θ)) [28][29][30]. In the yielding region where the neck of the specimen is formed, complicated deformation mechanism is expected.…”

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confidence: 99%

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Deformation mechanism of high-density polyethylene probed by in situ Raman spectroscopy

Kida

Oku

Hiejima

et al. 2015

Polymer

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Semi-crystalline polymers such as polyethylene (PE) and polypropylene (PP) show complicated morphologies composed of a mixture of crystalline and amorphous phases. The diversity in the structure with a wide range of length scales is responsible for the durability or high toughness of semi-crystalline polymers [1,2].When a high-density polyethylene (HDPE) specimen is uniaxially drawn, the elastic deformation is followed by double yield points referred to as the first and the second yields. During such dual plastic deformations, large-scale transformation of the semi-crystalline morphology takes place, and collapse of the spherulite structures, necking of the sample specimens, and rearrangement of the lamellar crystals and the polymer chains have been observed [1][2][3][4][5][6]. Although various models, such as the lamellar local-melting and recrystallization model [4,7], and the lamellar cluster model [3,[8][9][10], have been proposed for the deformation mechanism, such complicated changes in the hierarchical structures of semicrystalline polymers are still controversial.Spectroscopic techniques have been applied for the orientational behavior of PE during elongation [11][12][13][14][15][16][17]. The infrared (IR) spectroscopy has been applied intensively, and it has been established that the molecular chains in the crystalline and amorphous phases orientate toward the draw direction [11][12][13][14]. It has also been demonstrated that the orientation proceeds rapidly after the first yield, and gradually in the neck-propagation and the strain-hardening regions.However, the IR spectroscopy gives one orientation parameter 〈P 2 〉 which corresponds to the averaged orientation. For PE, the vibrations of the side chains, such as CH 2 twisting and wagging, are IR-active, and the skeletal vibrations of the C-C bonds are IR-inactive, then the load sharing on the polymer chains could not be directly observed with the IR spectroscopy.Raman spectroscopy has several advantages to investigate the deformation behavior of polymeric materials [18][19][20][21][22][23][24]: it is applicable to opaque and thick samples, and molecular environments can be separately detected for both the crystalline and the amorphous phases. Raman scattering is an optical technique that provides a complementary approach to IR absorption when transparent and very thin (typically <100 µm thickness) films are required. In addition, it is advantageous to use Raman spectroscopy because the vibrations of the skeletal C-C bonds in main chains are directly observed [20,25]. Because the C-C stretching vibration is strongly Raman active, microenvironments of the polymer chains are probed by the spectral shifts [26,27]. Polarized Raman spectroscopy gives not only a measure of the average orientation, which is obtained by the usual spectroscopies such as birefringence and IR dichrom, but also the orientation distribution function (ODF, N(θ)) [28][29][30]. In the yielding region where the neck of the specimen is formed, complicated deformation mechanism is expect...

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Section: Resultsmentioning

confidence: 98%

“…For PE, the symmetric C-C stretching mode at 1130 cm −1 is relevant. The integrated intensities of the polarized spectra are expressed as [20,29,40,41]. Fig.…”

Section: Tablementioning

confidence: 99%

mentioning

confidence: 99%

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Deformation mechanism of high-density polyethylene probed by in situ Raman spectroscopy

Kida

Oku

Hiejima

et al. 2015

Polymer

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“…Raman spectra at each « eng were recorded as A ∥ or A ⊥ , depending on whether the laser polarization was parallel or perpendicular, respectively, to the stretching direction. We calculated the hP 2 i coefficient from these amplitudes and refer to this coefficient as the molecular order parameter, 18,32). S mol is zero for a perfectly isotropic vibration.…”

Section: Significancementioning

confidence: 99%

Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites

Varol

Meng

Hosseinkhani

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Polymer nanocomposites-materials in which a polymer matrix is blended with nanoparticles (or fillers)-strengthen under sufficiently large strains. Such strain hardening is critical to their function, especially for materials that bear large cyclic loads such as car tires or bearing sealants. Although the reinforcement (i.e., the increase in the linear elasticity) by the addition of filler particles is phenomenologically understood, considerably less is known about strain hardening (the nonlinear elasticity). Here, we elucidate the molecular origin of strain hardening using uniaxial tensile loading, microspectroscopy of polymer chain alignment, and theory. The strain-hardening behavior and chain alignment are found to depend on the volume fraction, but not on the size of nanofillers. This contrasts with reinforcement, which depends on both volume fraction and size of nanofillers, potentially allowing linear and nonlinear elasticity of nanocomposites to be tuned independently.nanocomposites | nonlinear elasticity | strain stiffening | polymer bridging | polymer chain alignment M any synthetic and natural materials around us increase their elastic modulus upon large deformation after initial softening-a phenomenon that is known as work or strain hardening, which is critical to their function. In ductile polymer materials, the strain-hardening behavior is essential for their functional lifetime, resilience, and toughness-all key parameters of their practical uses-because these materials repetitively bear large loads (1, 2). Many industrial and consumer polymeric materials are composites, in which (hard) nanoscale inorganic particles, or fillers, are blended with polymer matrices to tailor their mechanical properties. In preparing such nanocomposites, filler−filler and filler−matrix interaction, filler dispersion, and polymer properties all affect the linear (low strain) and nonlinear (high strain) mechanical response in nontrivial ways (3). Although a massive volume of work has attempted to clarify the mechanism of reinforcement (increased linear elasticity) at low strain and of nonlinear strain softening (the Payne and Mullins effects) at medium strain, a comparatively much smaller body of work exists that focuses on the mechanism of strain hardening in polymer composite materials.In analogy to rubber elasticity at large deformations, strain hardening in polymer composites is typically attributed to the increasing resistance to deformation of extended and oriented polymer chains (4-7). However, it has been shown that polymer chain alignment during strain hardening is strongly affected by dispersing fillers within the host polymer matrix (8-10). To account for these observations, one needs to establish the relation between the macroscopically observed strain hardening and the microscopic chain alignment that is affected by the presence of fillers.The connection between chain alignment and strain hardening in glassy polymer composites is purported to occur because the fillers act as "entanglement attractors." In this...

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“…For PE sample, the Raman band at 1130 cm -1 assigned to the C-C symmetric stretching mode of crystalline chains has been used to obtain the orientation parameters [22,35]. In this study, two orientation parameters were determined from the intensities of three polarized Raman spectra as follows: [36][37][38][39] (1) (2) Here,  is the angle between the stretching direction and the principal axis of the Raman tensor. Moreover, the orientation distribution function (ODF) defined as the following equations was determined from the orientation parameters as [38,39] (3)…”

Section: Orientation Parametermentioning

confidence: 99%

Effect of Strain Rate on Microscopic Deformation Behavior of High-density Polyethylene under Uniaxial Stretching

2017

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Abstract. The microscopic deformation behaviors such as the load sharing and the molecular orientation of highdensity polyethylene under uniaxial stretching at various strain rates were investigated by using in-situ Raman spectroscopy. The chains within crystalline phase began to orient toward the stretching direction beyond the yielding region and the orientation behavior was not affected by the strain rate. While the stretching stress along the crystalline chains was also not affected by the strain rate, the peak shifts of the Raman bands at 1130, 1418, 1440 and 1460 cm -1 , which are sensitive to the interchain interactions obviously, depended on the strain rate; the higher strain rates lead to the stronger stretching stress or negative pressure on the crystalline and amorphous chains. These effects of the strain rate on the microscopic deformation was associated with the cavitation and the void formation leading to the release of the internal pressure.

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Accurate New Method for Molecular Orientation Quantification Using Polarized Raman Spectroscopy

Cited by 67 publications

References 47 publications

Deformation mechanism of high-density polyethylene probed by in situ Raman spectroscopy

Deformation mechanism of high-density polyethylene probed by in situ Raman spectroscopy

Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites

Effect of Strain Rate on Microscopic Deformation Behavior of High-density Polyethylene under Uniaxial Stretching

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