Table extends beyond right margin, how to autofit table to text width?

Question

\begin{table}[H]
\caption{Optimised combinations of hydrophobic-SiO\textsubscript{2} (H-SiO\textsubscript{2}) particles, fatty acid and solvent loadings for water repellent coating slurries. SiO\textsubscript{2} nanoparticles (10.00 wt\%) were functionalised with their respective fatty acid (2.00 wt\%)/ethanol (88.00 wt\%) mixture.}
\label{Paper_table}
\begin{center}


\begin{tabular}{|l|l|l|l|l|}
\hline 
\textbf{Fatty acid}  & \textbf{Carbon chain length} & \textbf{H-SiO\textsubscript{2} particle loading/wt\%} & \textbf{Fatty acid loading/wt\%} & \textbf{Ethanol loading/\%} \\ 
\hline 
Octanoic & 2 & 3 & 3 & 0.18 \\ 
\hline 
Decanoic & 2 & 3 & 3 & 0.18 \\ 
\hline 
Dodecanoic & 2 & 3 & 3 & 0.18 \\ 
\hline
Hexadecanoic & 2 & 3 & 3 & 0.18 \\ 
\hline
Octadecanoic & 2 & 3 & 3 & 0.18 \\ 
\hline

\end{tabular}
\end{center}

\end{table}

Answer 1

You can use the p column type to specify the width of your columns. May I suggest using the booktabs package for a nicer look and removing the vertical lines ? If you don't want the text to be centered, remove the >{\centering} from the code below.

\documentclass{article}

\usepackage{tabularx}
\usepackage{booktabs}

\begin{document}
\begin{table}[h] 
\caption{Optimised combinations of hydrophobic-SiO\textsubscript{2} (H-SiO\textsubscript{2}) particles, fatty acid and solvent loadings for water repellent coating slurries. SiO\textsubscript{2} nanoparticles (10.00 wt\%) were functionalised with their respective fatty acid (2.00 wt\%)/ethanol (88.00 wt\%) mixture.} 
\label{Paper_table} 
\begin{center}
\begin{tabular}{>{\centering}p{0.18\textwidth}>{\centering}p{0.12\textwidth}>{\centering}p{0.18\textwidth}>{\centering}p{0.18\textwidth}>{\centering\arraybackslash}p{0.15\textwidth}}
\toprule \textbf{Fatty acid} & \textbf{Carbon chain length} & \textbf{H-SiO\textsubscript{2} particle loading /wt\%} & \textbf{Fatty acid loading /wt\%} & \textbf{Ethanol loading /\%} \\
\midrule Octanoic & 2 & 3 & 3 & 0.18 \\
\midrule Decanoic & 2 & 3 & 3 & 0.18 \\
\midrule Dodecanoic & 2 & 3 & 3 & 0.18 \\
\midrule Hexadecanoic & 2 & 3 & 3 & 0.18 \\
\midrule Octadecanoic & 2 & 3 & 3 & 0.18 \\
\bottomrule
\end{tabular} 
\end{center}
\end{table}
\end{document}

Following this question, other possibilities include rotating the table.

Answer 2

I'd like to recommend that you use a tabularx environment, which allows automatic line wrapping for its X column type. I'd also like to recommend that you give the table a more "open" look, by getting rid of all vertical rules and employing fewer, but well-spaced horizontal rules. And, if you load the mhchem package, you can typeset the names of chemical compounds using the package's \ce macro.

\documentclass{article}
\usepackage{tabularx,ragged2e,booktabs,caption}
\newcolumntype{L}{>{\RaggedRight\arraybackslash}X}
\usepackage[version=4]{mhchem} % to typeset chemical compound names
\begin{document}

\begin{table}
\caption{Optimised combinations of hydrophobic-\ce{SiO2} (H-\ce{SiO2}) 
particles, fatty acid and solvent loadings for water repellent 
coating slurries.} 
\label{Paper_table}

\ce{SiO2} nanoparticles (10.00 wt\%) were functionalised with their 
respective fatty acid (2.00 wt\%)\slash ethanol (88.00 wt\%) mixture.

\smallskip
\begin{tabularx}{\textwidth}{@{} l *{4}{L} @{}}
\toprule 
\textbf{Fatty acid}  & 
\textbf{Carbon chain length} & 
\textbf{H-\ce{SiO2} particle loading\slash wt\%} & 
\textbf{Fatty acid loading\slash wt\%} & 
\textbf{Ethanol loading\slash\%} \\ 
\midrule 
Octanoic     & 2 & 3 & 3 & 0.18 \\  
Decanoic     & 2 & 3 & 3 & 0.18 \\ 
Dodecanoic   & 2 & 3 & 3 & 0.18 \\ 
Hexadecanoic & 2 & 3 & 3 & 0.18 \\ 
Octadecanoic & 2 & 3 & 3 & 0.18 \\ 
\bottomrule
\end{tabularx}
\end{table}
\end{document}