Single Molecule Force Spectroscopy Study on the Apparent Nanomechanical Properties of Polyethylene Single Crystals†

doi:10.7503/cjcu20170434

Abstract

Abstract:

Semi-crystalline polymers have been widely used as plastic, fiber and elastomers due to their excellent mechanical properties. As is well known, semi-crystalline polymer materials are composed of crystal and amorphous phases, and crystal phase plays very important roles in their mechanical properties. However, it is very difficult to discern the contribution of crystalline phase to the mechanical properties using traditional methods. Here, we study the mechanical properties of single polyethylene(PE) molecule within its single crystal using combined techniques of atomic force microscopy(AFM) imaging and AFM-based single-molecule force spectroscopy(SMFS). The results show that the apparent mechanical stability of single PE chain significantly increased with the increase of the thickness of PE single crystal. The stiffer loading device greatly enhanced the unfolding force of the single PE chain and promoted the formation of intermediates during unfolding process. These results deepen understanding on the origin of mechanical properties of PE single crystal, and may be useful for tuning the mechanical response of corresponding polymer materials.

Key words: Polyethylene single crystal, Atomic force microscopy, Single-molecule force spectroscopy, Nano-mechanical property

CLC Number:

O631.1⁺3

TrendMD:

LÜ Xiujuan, SONG Yu, ZHANG Wenke. Single Molecule Force Spectroscopy Study on the Apparent Nanomechanical Properties of Polyethylene Single Crystals^†[J]. Chem. J. Chinese Universities, 2018, 39(1): 166.

Figures/Tables 5

Fig.1 AFM images of PE single crystals prepared at different crystallization temperatureTc/℃: (A) 65; (B) 70; (C) 75; (D) 80.

Fig.2 Schematic illustration of the force-induced unfolding of single PE chain from its single crystal(A), typical force-extension curves obtained on PE single crystals prepared at Tc of 65 ℃(red), 70 ℃(blue), 75 ℃(green), 80 ℃(purple)(B) and histograms of length increments between adjacent peaks(C) and peak forces(D)Thickness/nm: a. 8; b. 10; c. 11; d. 12.

Fig.3 Typical small sawtooth-containing force-extension curves obtained on PE single crystal(A) and closer inspection of the small sawtooth peaks on the big peak(B)ΔLp: length increment between adjacent small peaks. Inset: histogram of ΔLp.

Fig.4 Typical force-extension curves obtained by cantilevers(A), histograms of peak forces(B), closer inspection of the small sawtooth peaks on the big peak(C) and spring constant effect on the relative width of small sawtooth peaks(D)Cantilever/(pN·nm-1): a. 40; b. 150; c. 600. ΔL*: width of sawtooth peaks on the big peak.

Fig.5 Typical force-extension curve divided into five parts according extension(A), histogram of peak forces(B), ΔL*/ΔL(C) and Ke(D)(A) 0—50 nm(red, a), 50—100 nm(yellow, b), 100—150 nm(green, c), 150—200 nm(blue, d), 200—250 nm(purple, e).(B) a. (507±221) pN; b. (462±236) pN; c. (443±195) pN; d. (337±138) pN; e. (247±185) pN.(C) a. (32±27)%; b. (16±19)%; c. (3.8±6.6)%; d. (3.2±4.3)%; e. (3.0±3.5)%;(D) a. (103±74) pN/nm; b. (53±40) pN/nm; c. (44±32) pN/nm; d. (40±30) pN/nm; e. (25±24) pN/nm.

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