Flow-induced precursors

Fig. 8.1. Schematic representation of flow-induced precursor structures at different stages (A) before shear, (B) formation of precursor structures containing linear nuclei (shish), (C) formation of shish-kebab morphology. (Reprinted with permission from [21])...

Models without a Flow-Induced Precursor Phase Flow-enhanced nucleation is in most cases described by an expression of the form... 

The epitaxial growth and the formation of a shish-kebab stmcture were also investigated in high molecular weight iPP (HMW-iPP)/low-molecular-weight LLDPE (LMW-LLDPE) blends [21]. The formation of the initial crystallization precursor structure was investigated by using synchrotron WAXS/SAXS techniques at 130 and 140 °C. Shear was applied at temperatures above the cloud points of these blends, and therefore, the HMW-iPP chains could form a flow-induced crystalline stmcture in the blends only at 6 and 9 wt% of HMW-iPP LMW-LLDPE merely served as the amorphous matrix (Fig. 5.3). When the HMW-iPP... 

J. K. Keum, Y. Mao, F. Zuo, B.S. Hsiao, Flow-induced crystallization precursor stmcture in high molecular weight isotactic polypropylene (HMW-iPP)/low molecular weight linear low density polyethylene (LMW-LLDPE) binary blends. Polymer 54, 1425-1431 (2013)... 

To understand the mechanism leading to enhancement of crystallization under shear, the structure of the so-call shish or row nuclei, the primary nucleus induced by flow, is essential. The common textbook picture is that the shish consist of extended-chain crystals that maybe defective [184-189]. It is generally accepted that structures with some degree of order are induced by the flow before the onset of crystallization, which can be long living at shallow supercooling [127-150]. These shear-induced precursors have been described... 

Role of Chain Entanglement Network on Formation of Flow-Induced Crystallization Precursor Structure... 

B.S. Hsiao Role of Chain Entanglement Network on Formation of Flow-Induced Crystallization Precursor Structure, Lect. Notes Phys. 714, 133-149 (2007)... 

Current Opinions on Flow-Induced Crystallization Precursor Structures... 

Somani R H, Yang L, Zhu L and Hsiao B S (2005) Flow-induced shish kebabs precursor structures in entangled polymer melts. Polymer 46 8587-8623. 

Somani RH, Yang L, Zhu L, Hsiao BS (2005) Flow-induced shish-kebab precursor structures in entangled polymer melts. Polymer 46 8587-8623 Sorrentino A, De Santis F, Titomanlio G (2007) Polymer crystallization under high cooling rate and pressure a step towards polymer processing conditions. Lect Notes Phys 714 329-344 Stocker W, Magonov SN, Cantow HI, Wittmann JC, Lotz B (1993) Contact faces of epitaxially crystallized a- and y-phase isotactic polypropylene observed by atomic force microscopy. Macromolecules 26 5915-5923... 

FAB and LSIMS are matrix-mediated desorption techniques that use energetic particle bombardment to simultaneously ionize samples like carotenoids and transfer them to the gas phase for mass spectrometric analysis. Molecular ions and/or protonated molecules are usually abundant and fragmentation is minimal. Tandem mass spectrometry with collision-induced dissociation (CID) may be used to produce abundant structurally significant fragment ions from molecular ion precursors (formed using FAB or any suitable ionization technique) for additional characterization and identification of chlorophylls and their derivatives. Continuous-flow FAB/LSIMS may be interfaced to an HPLC system for high-throughput flow-injection analysis or on-line LC/MS. 

The eventual products in reaction (1) have been identified as SO and MSA from experiments involving the steady photolysis of mixtures of DMS and a photolytic precursor of OH (4-91 Absolute measurements of lq have been obtained using the discharge-flow method with resonance fluorescence or electron paramagnetic resonance (EPR) detection of OH (10-141. and the flash photolysis method with resonance fluorescence or laser induced fluorescence (LIF) detection of OH (14-181. Competitive rate techniques where Iq is measured relative to the known rate constant for a reaction between OH and a reference organic compound (18-211 have also been employed to determine k at atmospheric pressure of air. 

Au nanocrystals were prepared as following 50 mg calcined mesoporous silica was immersed in 100 mL aqueous solution of HAuCl4-3H20 (3 mg / 100 mL). The solvent was evaporated in a rotary evaporator, and subsequently, 100 mL CH2CI2 was added to induce the outer surface bound metal precursors to move into the channels of mesoporous silica. CH2CI2 was also removed by evaporation. The obtained solids were dried at room temperature and reduced in a constant H2 flow at 773 K for 3 h. Silica frameworks were dissolved using a 10 wt% solution of HF to obtain unsupported Au nanoparticles. 

Figure 2. Workflow of an LC-MS/MS experiment. A mixture of peptides from a protein sample digest is separated by reversed-phase chromatography on a nano-flow HPLC. The peptides elute from the RP column and are ionized by an electrospray source. In the first stage of mass spectrometry, m/z values and charge states for each precursor ion are determined and the most abundant precursor ions are selected for analysis in the second stage. The ions are then fragmented with by collision-induced dissociation (CID) a gas to produce fragment ions which are detected. Using the mass (from MS-1) and sequence information (from MS-2) protein sequence databases are searched to provide peptide identifications and protein matches.

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