Using nanocapsules as building blocks to fabricate organic polymer nanofoam with ultra low thermal conductivity and high mechanical strength

doi:10.1016/j.polymer.2012.10.012

Polymer

Volume 53, Issue 25, 30 November 2012, Pages 5699-5705

https://doi.org/10.1016/j.polymer.2012.10.012 Get rights and content

Abstract

A new strategy using the performed nanocapsules with well-defined highly crosslinked polymer shell as building blocks was proposed to fabricate the organic polymeric nanofoam. This new strategy allowed us to fabricate the high performance organic polymeric nanofoam, for the first time, under normal drying conditions. The thermal conductivities of the nanofoams in the forms of powder and monolith were far lower than that of the stagnant air and half those of the standard commercial polymer foams. The nanofoam monoliths showed the crush strength up to 8.55 ± 2.10 MPa and compressive strain at break up to 45% ± 6%.

Graphical abstract

Section snippets

The nanocapsules and the nanofoam powder

The building blocks, nanocapsules, were synthesized by the interfacial reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization, which we invented recently [29], [30]. Miniemulsion is a dispersed system, where oil minidroplets of 30 nm–500 nm are kinetically stabilized by surfactant and co-stabilizer (some compound with extremely low water solubility) in water [31], [32]. Miniemulsion polymerization, where the polymer particles are directly converted from the monomer

Summary

We demonstrated that the high performance polymeric nanofoam of air could be fabricated, for the first time, at normal drying conditions in the forms of powder and monolith. The polymer nanofoam showed the ultra low thermal conductivity, only half those of the conventional polymer foam. The crush strength of the monolith of the polymer nanofoam was as high as 8.55 MPa. The compressive strain at break was 45%. The key for the success is to use the performed nanocapsules with well-defined highly

Preparation of nanocapsules

The nanocapsules were made by the interfacial RAFT miniemulsion polymerization according to the previous report [37]. The recipe to synthesize the nanocapsules used in each experiment is listed in Table 4. The conversion was close to 100%. The solid content of the final products was 20 wt%.

Preparation of the powders of the hollow nanocapsules

The product latex of nanocapsules was demulsified by HCl solution and re-dispersed in tetrahydrofuran (THF) with magnetic stirring for over 12 h to dissolve paraffin out of the nanocapsules. Then the

Acknowledgements

The authors would like to thank the financial support from National Natural Science Foundation (Grant No. 21125626, 21076181, 20836007) and Program for Changjiang Scholars and Innovative Research Team in University.

References (43)

R. Baetens et al.
Energ Build
(2011)
X. Lu et al.
J Non-Cryst Solids
(1995)
R.W. Pekala et al.
J Non-Cryst Solids
(1995)
G. Biesmans et al.
J Non-Cryst Solids
(1998)
J.K. Lee et al.
J Sol-Gel Sci Technol
(2009)
F. Fischer et al.
Polymer
(2006)
J.K. Lee et al.
J Sol-Gel Sci Technol
(2007)
P.B. Sarawade et al.
Appl Surf Sci
(2007)
B. Xu et al.
Microporous Mesoporous Mater
(2012)
S.D. Bhagat et al.
Microporous Mesoporous Mater
(2007)

O. Czakkel et al.

Microporous Mesoporous Mater

(2005)

Y. Luo et al.

Polymer

(2007)

F.N. Jones et al.

Prog Org Coat

(1994)

S. Tan et al.

Polymer

(2011)

A.C. Pierre et al.

Chem Rev

(2002)

N. Hüsing et al.

Angew Chem Int Ed

(1998)

C.A. Morris et al.

Science

(1999)

Energy efficiency, climate change and insulation....

E.L. Cussler et al.

Chemical product design

(2011)

X. Pekala et al.

Science

(1992)

S.S. Kistler

Nature

(1931)

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Using nanocapsules as building blocks to fabricate organic polymer nanofoam with ultra low thermal conductivity and high mechanical strength

Abstract

Graphical abstract

Section snippets

The nanocapsules and the nanofoam powder

Summary

Preparation of nanocapsules

Preparation of the powders of the hollow nanocapsules

Acknowledgements

Energ Build

J Non-Cryst Solids

J Non-Cryst Solids

J Non-Cryst Solids

J Sol-Gel Sci Technol

Polymer

J Sol-Gel Sci Technol

Appl Surf Sci

Microporous Mesoporous Mater

Microporous Mesoporous Mater

Microporous Mesoporous Mater

Polymer

Prog Org Coat

Polymer

Chem Rev

Angew Chem Int Ed

Science

Chemical product design

Science

Nature