Editing Soft matter (section)

== Classes of soft matter ==
[[File:DNA animation.gif|thumb|A portion of the [[Nucleic acid double helix|DNA double helix]], an example of a [[biopolymer]].]]
[[File:Inclusion complex.png|thumb|Host-guest complex of polyethylene glycol [[oligomer]] bound within an [[Cyclodextrin|α-cyclodextrin]] molecule; a common scaffold used in the formation of gels. The atoms are colored such that red represents oxygen, cyan represents carbon, and white represents hydrogen.]]
[[File:Liquid Crystal.png|thumb|Cartoon representation of the molecular order of crystal, liquid crystal, and liquid states.]]
Soft matter consists of a diverse range of interrelated systems and can be broadly categorized into certain classes. These classes are by no means distinct, as often there are overlaps between two or more groups.

=== Polymers ===
{{Main|Polymer}}
Polymers are large molecules composed of repeating subunits whose characteristics are governed by their environment and composition. Polymers encompass synthetic plastics, natural fibers and rubbers, and biological proteins. Polymer research finds applications in [[nanotechnology]],<ref>{{Cite journal |last1=Mashaghi |first1=Samaneh |last2=Jadidi |first2=Tayebeh |last3=Koenderink |first3=Gijsje|author3-link=Gijsje Koenderink |last4=Mashaghi |first4=Alireza |date=2013-02-21 |title=Lipid Nanotechnology |journal=International Journal of Molecular Sciences |language=en |volume=14 |issue=2 |pages=4242–4282 |doi=10.3390/ijms14024242 |issn=1422-0067 |pmc=3588097 |pmid=23429269|doi-access=free }}</ref><ref>{{Cite journal |last=Hamley |first=Ian W. |date=2003 |title=Nanotechnology with Soft Materials |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.200200546 |journal=Angewandte Chemie International Edition |volume=42 |issue=15 |pages=1692–1712 |doi=10.1002/anie.200200546|pmid=12707884 }}</ref> from [[materials science]] and [[drug delivery]] to [[protein crystallization]].<ref name=":2" /><ref name=":11">{{Cite journal |last1=Maimouni |first1=Ilham |last2=Cejas |first2=Cesare M. |last3=Cossy |first3=Janine |last4=Tabeling |first4=Patrick |last5=Russo |first5=Maria |date=2020 |title=Microfluidics Mediated Production of Foams for Biomedical Applications |journal=Micromachines |language=en |volume=11 |issue=1 |pages=83 |doi=10.3390/mi11010083 |issn=2072-666X |pmc=7019871 |pmid=31940876|doi-access=free }}</ref>

=== Foams ===
{{Main|Foam}}
Foams consist of a liquid or solid through which a [[gas]] has been dispersed to form cavities.  This structure imparts a large [[surface-area-to-volume ratio]] on the system.<ref name=":10" /><ref name=":12">{{Cite journal |last1=Jin |first1=Fan-Long |last2=Zhao |first2=Miao |last3=Park |first3=Mira |last4=Park |first4=Soo-Jin |date=2019 |title=Recent Trends of Foaming in Polymer Processing: A Review |journal=Polymers |language=en |volume=11 |issue=6 |pages=953 |doi=10.3390/polym11060953 |issn=2073-4360 |pmc=6631771 |pmid=31159423|doi-access=free }}</ref> Foams have found applications in [[Thermal insulation|insulation]] and [[Textile|textiles]],<ref name=":12" /> and are undergoing active research in the biomedical field of drug delivery and [[tissue engineering]].<ref name=":11" />  Foams are also used in automotive for water and dust sealing and noise reduction. 

=== Gels ===
{{Main|Gel}}
Gels consist of non-solvent-[[Solubility|soluble]] 3D polymer scaffolds, which are [[Covalent bond|covalently]] or physically [[Cross-link|cross-linked]], that have a high solvent/content ratio.<ref>{{Cite journal |last=Ahmed |first=Enas M. |date=2015 |title=Hydrogel: Preparation, characterization, and applications: A review |journal=Journal of Advanced Research |language=en |volume=6 |issue=2 |pages=105–121 |doi=10.1016/j.jare.2013.07.006 |pmc=4348459 |pmid=25750745}}</ref><ref name=":13">{{Cite journal |last1=Qi |first1=Zhenhui |last2=Schalley |first2=Christoph A. |date=2014-07-15 |title=Exploring Macrocycles in Functional Supramolecular Gels: From Stimuli Responsiveness to Systems Chemistry |url=https://pubs.acs.org/doi/10.1021/ar500193z |journal=Accounts of Chemical Research |language=en |volume=47 |issue=7 |pages=2222–2233 |doi=10.1021/ar500193z |pmid=24937365 |issn=0001-4842}}</ref> Research into functionalizing gels that are sensitive to mechanical and thermal stress, as well as solvent choice, has given rise to diverse structures with characteristics such as [[Shape-memory polymer|shape-memory]],<ref>{{Cite journal |last1=Korde |first1=Jay M. |last2=Kandasubramanian |first2=Balasubramanian |date=2020 |title=Naturally biomimicked smart shape memory hydrogels for biomedical functions |url=https://linkinghub.elsevier.com/retrieve/pii/S1385894719318339 |journal=Chemical Engineering Journal |language=en |volume=379 |pages=122430 |doi=10.1016/j.cej.2019.122430|bibcode=2020ChEnJ.37922430K |s2cid=201216064 }}</ref> or the ability to bind [[Host–guest chemistry|guest]] molecules selectively and reversibly.<ref name=":13" />

=== Colloids ===
{{Main|Colloid}}
Colloids are non-soluble particles suspended in a medium, such as proteins in an aqueous solution.<ref name=":16">{{Cite journal |last1=Hamley |first1=Ian W. |last2=Castelletto |first2=Valeria |date=2007-06-11 |title=Biological Soft Materials |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.200603922 |journal=Angewandte Chemie International Edition |language=en |volume=46 |issue=24 |pages=4442–4455 |doi=10.1002/anie.200603922|pmid=17516592 }}</ref> Research into colloids is primarily focused on understanding the organization of matter, with the large structures of colloids, relative to individual molecules, large enough that they can be readily observed.<ref>{{Cite journal |last=Manoharan |first=Vinothan N. |date=2015-08-28 |title=Colloidal matter: Packing, geometry, and entropy |journal=Science |language=en |volume=349 |issue=6251 |pages=1253751 |doi=10.1126/science.1253751 |pmid=26315444 |s2cid=5727282 |issn=0036-8075|doi-access=free }}</ref>

=== Liquid crystals ===
{{Main|Liquid crystal}}
Liquid crystals can consist of proteins, small molecules, or polymers, that can be manipulated to form cohesive order in a specific direction.<ref name=":4">{{Cite journal |last1=Bisoyi |first1=Hari Krishna |last2=Li |first2=Quan |date=2022-03-09 |title=Liquid Crystals: Versatile Self-Organized Smart Soft Materials |url=https://pubs.acs.org/doi/10.1021/acs.chemrev.1c00761 |journal=Chemical Reviews |language=en |volume=122 |issue=5 |pages=4887–4926 |doi=10.1021/acs.chemrev.1c00761 |pmid=34941251 |issn=0009-2665}}</ref> They exhibit liquid-like behavior in that they can [[Fluid dynamics|flow]], yet they can obtain close-to-crystal alignment. One feature of liquid crystals is their ability to [[Spontaneous symmetry breaking|spontaneously break symmetry]].<ref>{{Cite journal |last=Tschierske |first=Carsten |date=2018-12-08 |title=Mirror symmetry breaking in liquids and liquid crystals |journal=Liquid Crystals |language=en |volume=45 |issue=13–15 |pages=2221–2252 |doi=10.1080/02678292.2018.1501822 |s2cid=125652009 |issn=0267-8292|doi-access=free |bibcode=2018LoCr...45.2221T }}</ref> Liquid crystals have found significant applications in optical devices such as [[Liquid-crystal display|liquid-crystal displays]] (LCD).

=== Biological membranes ===
{{Main|Biological membrane}}
Biological membranes consist of individual [[phospholipid]] molecules that have self-assembled into a [[Lipid bilayer|bilayer]] structure due to [[Non-covalent interaction|non-covalent interactions]]. The localized, low energy associated with the forming of the [[membrane]] allows for the elastic deformation of the large-scale structure.<ref name=":17">{{Cite journal |last=Brown |first=Michael F. |date=2017-05-22 |title=Soft Matter in Lipid–Protein Interactions |url=https://www.annualreviews.org/doi/10.1146/annurev-biophys-070816-033843 |journal=Annual Review of Biophysics |language=en |volume=46 |issue=1 |pages=379–410 |doi=10.1146/annurev-biophys-070816-033843 |pmid=28532212 |issn=1936-122X}}</ref>