search.noResults

search.searching

note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
Cryo-Ultramicrotomy


by cryo-ultramicrotomy. The viscous high-concentration solution made it challenging to achieve an electron- transparent thin film using the Vitrobot plunge freezer. But in some local regions, we could still observe the side-views of straight aggregates with ~2.0 nm spacing ( Figure 5b insert). In general, cryo-sectioned specimens lead to sufficient image quality for identifying the side-view ( Figure 5c ) and top-view of the aggregates (not shown). Another intriguing feature revealed by CEMOVIS is the local orientation variation of the aggregates ( Figure 5c ), which is considered to be more realistic for the bulk material. But some pronounced specimen damage (crevasses, knife marks, compression, etc.) due to sample-knife interaction can often be seen ( Figure 5c ) and leads to a lower imaging quality at high resolution compared to the results from thin film plunge freezing. This current disadvantage of the bulk approach can be partially overcome by adding a cryoprotectant (for example, dextran) to the solution [ 2 ]. Figure 6 shows CEMOVIS images of 15% DSCG with 10% dextran. Dextran, a commonly used cryoprotectant to facilitate the vitrification process, was added to avoid water crystallization and to improve the cryo-sectioning quality. Columnar aggregates parallel ( Figure 6a ) and perpendicular ( Figure 6b ) to the specimen surface can be identified more easily because of considerably reduced sectioning damage compared to the results without dextran ( Figure 5c ). In addition, the improved imaging quality leads to better visibility of domains with random aggregate orientations and other detailed structures. Figure 6c shows bending and director variation in the aggregates, especially near domain boundaries. It should be mentioned that cryoprotectants act as depletion agents and compete for water. Polarized light microscopy (PLM) was employed to understand the impact of cryoprotectants on LC phase transition and to verify that the cryo-TEM results can still represent the native structure [ 4 ].


Figure 5 : (a) A schematic of nematic lyotropic chromonic LC. (b) Cryo-TEM of plunge-frozen nematic 6-hydroxy-5-[(4-sulfophenyl)azo]-2-naphthalenesulfonic acid (SSY) thin fi lm. The inset is a magnifi ed image of the local area marked by the square. (c) CEMOVIS of the same nematic SSY solution, showing variation of the local orientation of the aggregates. The arrows indicate crevasses introduced by cryo-ultramicrotomy. The inset is a magnifi ed image of the local area marked by the square. The dotted yellow lines in (b) and (c) indicate the orientations of local directors.


2018 March • www.microscopy-today.com


Liquid crystal–nanoparticle composites . Nanoparticle- doped LCs is an emerging area generating both fundamental and application interest. The physical properties of LCs and nanoparticles, including LC molecular alignment and metal nanoparticle surface plasmon resonance, can be tuned through the interaction between the anisotropic LC fluids and doped nanoparticles [ 8 ]. One of the challenges in LC-nanoparticle composites is that nanoparticles often aggregate into clusters [ 4 ]. Recently, photoresponsive azo thiol was used to passivate Au nanoparticles in 4-Cyano-4’- pentylbiphenyl for a homogeneous dispersion [ 8 ]. Figures 7 a and 7 b show comparative cryo-TEM results of the composite using thin film and bulk approaches, respectively. In the suspended 5CB thin films (including the sectioned slice in Figure 7b ), the doped Au nanoparticles (1–3 nm in diameter) are distributed randomly without agglomeration, which is a key determining factor for the composite properties including a stable reversible alignment control of 5CB molecules using light irradiation [ 8 ]. However, the carbon supporting film used in the thin film approach exhibits a strong attraction to


37


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76